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Expanding Spectrum of Mast Cell Activation Disorders: Monoclonal and Idiopathic Mast Cell Activation Syndromes

      Abstract

      Background

      In recent years, 2 new syndromes of mast cell activation have been described in patients with episodes of mast cell mediator release that range from flushing and abdominal cramping to anaphylaxis: monoclonal mast cell activation syndrome (MMAS) and idiopathic mast cell activation syndrome (MCAS).

      Objective

      This review will discuss these 2 new syndromes in the larger context of mast cell activation disorders as well as the diagnostic and treatment approaches for these conditions.

      Methods

      PubMed was searched using the following terms: mast cell activation disorder, mast cell activation syndrome, and clonal mast cell. Only English-language articles published up until February 27, 2013, were considered.

      Results

      MMAS has been diagnosed in patients with systemic reactions to hymenoptera stings and elevated baseline serum tryptase as well as in patients with unexplained episodes of anaphylaxis. A bone marrow biopsy establishes the diagnosis by revealing the presence of monoclonal mast cells that carry the D816V KIT mutation and/or express CD25 while the diagnostic requirements for systemic mastocytosis are not met. MCAS affects predominantly women in whom no mast cell abnormality or external triggers account for their episodes of mast cell activation. MCAS is a diagnosis of exclusion, and primary and secondary mast cell activation disorders as well as idiopathic anaphylaxis have to be ruled out before making the diagnosis. Patients with MCAS and MMAS are treated in a stepwise fashion with drugs that block the effects of mediators released by mast cells on activation. One third of MCAS patients experience complete resolution of symptoms with treatment, while one third have a major response and one third a minor response to treatment. A combination of drugs is usually necessary to achieve symptom control. No drug trial has been performed in patients with MMAS and MCAS.

      Conclusions

      MMAS and MCAS are 2 newly described, rare syndromes of mast cell activation. Further studies will be necessary to better understand the cause of these conditions and their natural evolution and to validate and improve the treatment approach. Research should also focus on developing drugs with the potential to cure these debilitating disorders. To achieve these goals, centers with expertise in mast cell activation disorders are essential as they allow for a critical mass of these patients to be enrolled in studies while providing those patients with the most up-to-date diagnostic procedures and treatment strategies.

      Key words

      Introduction

      Anaphylaxis is the most dramatic clinical reaction mediated by mast cells. It is characterized by the sudden onset of skin, cardiovascular, respiratory, gastrointestinal (GI), and neuromuscular symptoms and can rapidly lead to death.
      • Lieberman P.
      • Nicklas R.A.
      • Oppenheimer J.
      • et al.
      The diagnosis and management of anaphylaxis practice parameter: 2010 update.
      Although it is widely known that mast cells are activated in the context of an allergic reaction by the allergen-induced cross-linking of surface immunoglobulin (Ig) E/FcεRI (the high-affinity receptor for the Fc region of IgE), it should be recognized that many other stimuli and conditions can cause mast cell activation and therefore lead to anaphylaxis.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      In this regard, 2 new syndromes pertaining to mast cell activation have recently been described and deserve special attention: monoclonal and idiopathic mast cell activation syndrome, abbreviated respectively as MMAS and MCAS.
      From a clinical standpoint, MMAS and MCAS share many similarities with systemic mastocytosis (SM), a primary disorder of mast cells in which patients experience symptoms ranging from pruritus and flushing to anaphylaxis.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      SM is caused in >90% of patients by the D816V c-KIT gain-of-function somatic mutation.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      • Akin C.
      • Valent P.
      • Metcalfe D.D.
      Mast cell activation syndrome: proposed diagnostic criteria.
      The c-KIT gene codes for the transmembrane receptor KIT, which transmits signal on engaging its ligand, stem cell factor, and affects growth, differentiation, apoptosis, and activation of mast cells.
      • Metcalfe D.D.
      Mast cells and mastocytosis.
      Therefore, in patients with SM, mast cells are found to be morphologically and functionally abnormal and increased in numbers through clonal expansion.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      Recently, several groups identified patients with either “idiopathic anaphylaxis” (IA) or systemic reactions to hymenoptera stings in whom mast cells showed clonal abnormalities, alike those seen in SM, but that failed to meet its diagnostic requirements.
      • Akin C.
      • Scott L.M.
      • Kocabas C.N.
      • et al.
      Demonstration of an aberrant mast-cell population with clonal markers in a subset of patients with “idiopathic” anaphylaxis.
      • Bonadonna P.
      • Perbellini O.
      • Passalacqua G.
      • et al.
      Clonal mast cell disorders in patients with systemic reactions to Hymenoptera stings and increased serum tryptase levels.
      • Alvarez-Twose I.
      • Gonzalez de Olano D.
      • Sanchez-Munoz L.
      • et al.
      Clinical, biological, and molecular characteristics of clonal mast cell disorders presenting with systemic mast cell activation symptoms.
      • Alvarez-Twose I.
      • Gonzalez-de-Olano D.
      • Sanchez-Munoz L.
      • et al.
      Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
      • Sonneck K.
      • Florian S.
      • Mullauer L.
      • et al.
      Diagnostic and subdiagnostic accumulation of mast cells in the bone marrow of patients with anaphylaxis: monoclonal mast cell activation syndrome.
      The denomination of MMAS was chosen to characterize this syndrome, which importantly does not appear to simply be an early form of SM.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      • Akin C.
      • Valent P.
      • Metcalfe D.D.
      Mast cell activation syndrome: proposed diagnostic criteria.
      In another category of patients with evidence of episodic mast cell activation, investigators have failed to find any mast cell abnormality or external triggers that could explain those episodes.
      • Alvarez-Twose I.
      • Gonzalez de Olano D.
      • Sanchez-Munoz L.
      • et al.
      Clinical, biological, and molecular characteristics of clonal mast cell disorders presenting with systemic mast cell activation symptoms.
      • Alvarez-Twose I.
      • Gonzalez-de-Olano D.
      • Sanchez-Munoz L.
      • et al.
      Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
      • Hamilton M.J.
      • Hornick J.L.
      • Akin C.
      • et al.
      Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
      In 2010, Akin et al
      • Akin C.
      • Valent P.
      • Metcalfe D.D.
      Mast cell activation syndrome: proposed diagnostic criteria.
      proposed diagnostic criteria for this syndrome, which was named MCAS. It requires objective evidence of mast cell activation and exclusion of any other known mast cell activation disorder.
      • Akin C.
      • Valent P.
      • Metcalfe D.D.
      Mast cell activation syndrome: proposed diagnostic criteria.
      Its diagnostic criteria have recently been endorsed by an international consensus.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      This review will discuss these 2 new syndromes, MMAS and MCAS, in the larger context of mast cell activation disorders as well as the diagnostic and treatment approaches for these disorders.

      Materials and Methods

      PubMed was searched using the following terms: mast cell activation disorder, mast cell activation syndrome, and clonal mast cell. Only English-language articles published up until February 27, 2013, were considered.

      Results

      Three retrospective cohort studies provided clinical and laboratory data on patients with MCAS, and 1 gave information on their responses to treatment.
      • Alvarez-Twose I.
      • Gonzalez de Olano D.
      • Sanchez-Munoz L.
      • et al.
      Clinical, biological, and molecular characteristics of clonal mast cell disorders presenting with systemic mast cell activation symptoms.
      • Alvarez-Twose I.
      • Gonzalez-de-Olano D.
      • Sanchez-Munoz L.
      • et al.
      Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
      • Hamilton M.J.
      • Hornick J.L.
      • Akin C.
      • et al.
      Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
      Patients with MMAS were described in 5 retrospective studies, which mainly detailed their laboratory features, and none provided data on treatment.
      • Akin C.
      • Scott L.M.
      • Kocabas C.N.
      • et al.
      Demonstration of an aberrant mast-cell population with clonal markers in a subset of patients with “idiopathic” anaphylaxis.
      • Bonadonna P.
      • Perbellini O.
      • Passalacqua G.
      • et al.
      Clonal mast cell disorders in patients with systemic reactions to Hymenoptera stings and increased serum tryptase levels.
      • Alvarez-Twose I.
      • Gonzalez de Olano D.
      • Sanchez-Munoz L.
      • et al.
      Clinical, biological, and molecular characteristics of clonal mast cell disorders presenting with systemic mast cell activation symptoms.
      • Alvarez-Twose I.
      • Gonzalez-de-Olano D.
      • Sanchez-Munoz L.
      • et al.
      Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
      • Sonneck K.
      • Florian S.
      • Mullauer L.
      • et al.
      Diagnostic and subdiagnostic accumulation of mast cells in the bone marrow of patients with anaphylaxis: monoclonal mast cell activation syndrome.

      Mast Cell Activation Disorders: Diagnostic Criteria and Differential Diagnosis

      The clinical features of mast cell activation disorders result from the actions of the various mediators released by mast cells following their activation (Table I).
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      • Castells M.
      • Austen K.F.
      Mastocytosis: mediator-related signs and symptoms.
      • Triggiani M.
      • Patella V.
      • Staiano R.I.
      • et al.
      Allergy and the cardiovascular system.
      • Seidel H.
      • Molderings G.J.
      • Oldenburg J.
      • et al.
      Bleeding diathesis in patients with mast cell activation disease.
      • Prieto-Garcia A.
      • Zheng D.
      • Adachi R.
      • et al.
      Mast cell restricted mouse and human tryptase/heparin complexes hinder thrombin-induced coagulation of plasma and the generation of fibrin by proteolytically destroying fibrinogen.
      However, none of these are specific for mast cell activation, and many other conditions need to be considered in the differential diagnosis. Therefore, a comprehensive clinical history, physical examination, and basic laboratory tests are crucial in the patient evaluation. Some rather rare diseases and some more common ones deserve special consideration (Table II).
      • Nussberger J.
      • Cugno M.
      • Cicardi M.
      Bradykinin-mediated angioedema.
      Table IMast cell mediator–related symptoms in mast cell activation disorders.
      MediatorClinical Features
      HistamineHeadache, hypotension, pruritus, urticaria, angioedema, diarrhea, anaphylaxis
      TryptaseBleeding diathesis,
      Hematoma formation, bruising, prolonged bleeding after biopsies, gingival bleeding, epistaxis, gastrointestinal hemorrhage, conjunctival hemorrhage, or hemorrhagic ulcer disease was observed in 48.5% of patients with a mast cell activation disorder in a cohort of 68 patients.14
      ,
      Tryptase causes fibrinogen lysis.15
      inflammation
      Chymase
      Chymase induces angiotensin II synthesis.13
      Cardiac arrhythmias, myocardial infarction, hypertension
      Proteoglycans (heparin)Bleeding diathesis
      Hematoma formation, bruising, prolonged bleeding after biopsies, gingival bleeding, epistaxis, gastrointestinal hemorrhage, conjunctival hemorrhage, or hemorrhagic ulcer disease was observed in 48.5% of patients with a mast cell activation disorder in a cohort of 68 patients.14
      PAFAbdominal cramping, pulmonary edema, urticaria, bronchoconstriction, hypotension, arrhythmia, anaphylaxis
      Prostaglandin D2Flushing, mucus secretion, bronchoconstriction, vascular instability, headache, “mixed organic brain syndrome” (poor concentration, memory loss), nausea, abdominal pain
      CysLT (LTC4, LTD4, and LTE4)Mucus secretion, bronchoconstriction, vascular instability
      Cytokines (IL-1β, IL-6, TNF-α) and chemokinesConstitutional symptoms (fatigue), inflammation, osteoporosis
      Renin13Cardiac arrhythmias, myocardial infarction
      CysLT = cysteinyl leukotrienes; IL = interleukin; LTC4 = leukotriene C4; LTD4 = leukotriene D4; LTE4 = leukotriene E4; PAF = platelet activation factor; TNF = tumor necrosis factor.
      low asterisk Hematoma formation, bruising, prolonged bleeding after biopsies, gingival bleeding, epistaxis, gastrointestinal hemorrhage, conjunctival hemorrhage, or hemorrhagic ulcer disease was observed in 48.5% of patients with a mast cell activation disorder in a cohort of 68 patients.
      • Seidel H.
      • Molderings G.J.
      • Oldenburg J.
      • et al.
      Bleeding diathesis in patients with mast cell activation disease.
      Tryptase causes fibrinogen lysis.
      • Prieto-Garcia A.
      • Zheng D.
      • Adachi R.
      • et al.
      Mast cell restricted mouse and human tryptase/heparin complexes hinder thrombin-induced coagulation of plasma and the generation of fibrin by proteolytically destroying fibrinogen.
      Chymase induces angiotensin II synthesis.
      • Triggiani M.
      • Patella V.
      • Staiano R.I.
      • et al.
      Allergy and the cardiovascular system.
      Table IISelected differential diagnosis of mast cell activation disorders.
      Differential DiagnosisUseful Test(s) in Investigation
      Flushing
       MenopauseFSH, LH, estrogen
       Carcinoid syndrome24-Hour urine 5-hydroxyindoleacteic acid
       Pheochromocytoma24-Hour urine fractionated catecholamines and metanephrines
       Medullary carcinoma of the thyroidSerum calcitonin
      Cardiovascular (presyncope/syncope, tachycardia, hypotension)
       Postural tachycardia syndrome (POTS)Tilt table test
       Autonomic dysfunctionOrthostatic drop in blood pressure
       Cardiovascular diseases (arrhythmia)ECG
      Respiratory symptoms (throat tightness, stridor, wheezing)
       AsthmaPulmonary function tests
       Vocal cord dysfunctionLaryngoscopy, spirometry
       Hereditary and acquired angioedemaC4, C1q, C1 inhibitor antigenic and functional levels
       ACE inhibitor–associated angioedemaPlasma bradykinin
      Plasma bradykinin is elevated in ACE inhibitor–associated angioedema and hereditary and acquired angioedema, whereas it is normal in mast cell–related angioedema.16 Test not currently available. Diagnosis of ACE inhibitor–associated angioedema is based on history.
      Gastrointestinal symptoms (diarrhea, abdominal cramping)
       Primary bowel disease (irritable bowel syndrome, inflammatory bowel disease)Endoscopy and biopsy
       Neuroendocrine tumorsSerum vasoactive intestinal peptide
      Other
       Panic attackPsychiatric consultation
      ACE = angiotensin-converting enzyme; FSH = follicle-stimulating hormone; LH = luteinizing hormone.
      low asterisk Plasma bradykinin is elevated in ACE inhibitor–associated angioedema and hereditary and acquired angioedema, whereas it is normal in mast cell–related angioedema.
      • Nussberger J.
      • Cugno M.
      • Cicardi M.
      Bradykinin-mediated angioedema.
      Test not currently available. Diagnosis of ACE inhibitor–associated angioedema is based on history.
      Many diseases can cause flushing, which is very common in patients with mast cell activation disorders, and, although accompanying signs and symptoms are helpful in excluding some of them, it is often necessary to order additional tests.
      • Cardet J.C.
      • Castells M.C.
      • Hamilton M.J.
      Immunology and clinical manifestations of non-clonal mast cell activation syndrome.
      Carcinoid tumors release many mediators in an episodic fashion, some of them being also released by mast cells on activation (eg, histamine [H], prostaglandins).
      • Modlin I.M.
      • Kidd M.
      • Latich I.
      • et al.
      Current status of gastrointestinal carcinoids.
      This partly explains their similar clinical features (flushing, bronchospasm, diarrhea, hypotension) and that they can both respond to antihistamines.
      • Roberts 2nd, L.J.
      • Marney Jr, S.R.
      • Oates J.A.
      Blockade of the flush associated with metastatic gastric carcinoid by combined histamine H1 and H2 receptor antagonists Evidence for an important role of H2 receptors in human vasculature.
      This diagnosis can usually be excluded based on a normal 24-hour urine 5-hydroxyindoleacetic acid level.
      • Modlin I.M.
      • Kidd M.
      • Latich I.
      • et al.
      Current status of gastrointestinal carcinoids.
      Whereas the classic triad of headache, sweating, and tachycardia with hypertension readily orients toward a diagnosis of pheochromocytoma, most patients with this condition present with an incomplete triad and with symptoms suggestive of mast cell activation.
      • Bravo E.L.
      Pheochromocytoma: new concepts and future trends.
      Measurement of 24-hour urine fractionated metanephrines and catecholamines is a highly sensitive and specific diagnostic test for this disorder.
      • Perry C.G.
      • Sawka A.M.
      • Singh R.
      • et al.
      The diagnostic efficacy of urinary fractionated metanephrines measured by tandem mass spectrometry in detection of pheochromocytoma.
      Medullary cancer of the thyroid can cause flushing and diarrhea in patients with advanced disease, at which time they usually also show signs and symptoms of local involvement and have an increased serum calcitonin level.
      • Strosberg J.R.
      Update on the management of unusual neuroendocrine tumors: pheochromocytoma and paraganglioma, medullary thyroid cancer and adrenocortical carcinoma.
      Patients with postural tachycardia syndrome are frequently young women who experience many symptoms reminiscent of mast cell activation (lightheadedness, fatigue, anxiety, dyspnea, palpitations, and even syncope) on standing.
      • Thieben M.J.
      • Sandroni P.
      • Sletten D.M.
      • et al.
      Postural orthostatic tachycardia syndrome: the Mayo clinic experience.
      Moreover, superimposed mast cell activation has been described in a subgroup of those patients who experience flushing during episodes, as evidenced by elevated urinary methylhistamine levels.
      • Shibao C.
      • Arzubiaga C.
      • Roberts 2nd, L.J.
      • et al.
      Hyperadrenergic postural tachycardia syndrome in mast cell activation disorders.
      Treatment with H1- and H2-blockers as well as methyldopa was shown to be beneficial for this particular and rare subgroup, whereas β-blockers caused exacerbations in some of them.
      • Shibao C.
      • Arzubiaga C.
      • Roberts 2nd, L.J.
      • et al.
      Hyperadrenergic postural tachycardia syndrome in mast cell activation disorders.
      This finding highlights the need to differentiate this subgroup with associated mast cell activation from the larger group of patients with POTS who generally benefit from β-blockers and on which antihistamines have no effect.
      • Shibao C.
      • Arzubiaga C.
      • Roberts 2nd, L.J.
      • et al.
      Hyperadrenergic postural tachycardia syndrome in mast cell activation disorders.
      Respiratory symptoms are rarely predominant in patients with mast cell activation disorders and therefore several other conditions deserve careful consideration in patients with a predominance of those symptoms.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      In patients with isolated upper respiratory symptoms, direct visualization of the larynx is often key to determine the nature of the obstruction, which can range from vocal cord dysfunction to angioedema. Patients with predominant GI symptoms often need to be evaluated by a gastroenterologist, who can perform endoscopic procedures and biopsies that might be necessary to exclude primary bowel diseases. Finally, psychiatric disorders such as panic attacks should not be overlooked and require psychiatric evaluation after exclusion of all other causes.
      To attribute signs and symptoms to a mast cell activation disorder, the following three criteria should be fulfilled, as proposed by an international consensus
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      :
      Typical signs and symptoms of mast cell mediator release (affecting at least 2 organ systems)
      • Skin: flushing, pruritus, urticaria, angioedema
      • Cardiovascular: hypotension
      • Respiratory: wheezing, throat swelling
      • GI: diarrhea
      • Naso-ocular: pruritus
      Objective evidence of mediator release
      • Elevated serum tryptase: 20% + 2 ng/mL above baseline
      • Elevated 24-hour urinary histamine metabolites (methylhistamine)
      • Elevated 24-hour urinary prostaglandins (prostaglandin D2; 11β platelet-derived growth factor 2α)
      Response to therapy that blocks mast cell mediator activity
      • H1-receptor with or without H2-blockers, ketotifen, cromolyn sodium, aspirin, and leukotriene receptor antagonists
      The objective confirmation of mediator release is especially important to avoid misdiagnosing a mast cell activation disorder in patients with nonspecific signs and symptoms.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      • Akin C.
      • Valent P.
      • Metcalfe D.D.
      Mast cell activation syndrome: proposed diagnostic criteria.
      Serum tryptase, which is widely available and highly reproducible, is considered the preferred mean to ascertain mast cell activation, with the drawback that its level must be measured between 15 minutes and 4 hours after an event.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      • Schwartz L.B.
      • Bradford T.R.
      • Rouse C.
      • et al.
      Development of a new, more sensitive immunoassay for human tryptase: use in systemic anaphylaxis.
      To determine whether a significant increase in tryptase occurred with the symptomatic event, a baseline value has to be measured, usually at least 24 hours after symptom resolution.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      The increase in tryptase should be of at least 20% + 2 ng/mL above baseline to be considered significant (eg, if baseline is 10 ng/mL, a level ≥14 ng/mL would be significant).
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      The baseline tryptase value can also be used to determine the mast cell burden. Indeed, most patients with SM have a value >20 ng/mL, which is a minor diagnostic criterion of the disease, whereas in MCAS, Hamilton et al
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      • Hamilton M.J.
      • Hornick J.L.
      • Akin C.
      • et al.
      Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
      reported that only 33% of patients had an elevated baseline level (>11.4 ng/mL). In MMAS the value can either be normal or elevated; a mean level of 18.3 ng/mL was reported in 1 cohort.
      • Alvarez-Twose I.
      • Gonzalez-de-Olano D.
      • Sanchez-Munoz L.
      • et al.
      Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
      Other less well-validated methods of documenting mast cell activation include measurement of 24-hour urine methylhistamine or prostaglandins (prostaglandin D2 or 11β platelet-derived growth factor 2α), although the significant level of increase for those markers has not been established.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      • Hogan A.D.
      • Schwartz L.B.
      Markers of mast cell degranulation.
      • Awad J.A.
      • Morrow J.D.
      • Roberts 2nd, L.J.
      Detection of the major urinary metabolite of prostaglandin D2 in the circulation: demonstration of elevated levels in patients with disorders of systemic mast cell activation.
      On the other hand, the baseline levels were found to be elevated in a majority of patients with MCAS, although very few patients had baseline elevations in >1 mediator.
      • Hamilton M.J.
      • Hornick J.L.
      • Akin C.
      • et al.
      Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
      Finally, it is important to document clinical improvement with antimediator therapy, particularly antihistamines or other mast cell stabilizing agents such as cromolyn sodium or ketotifen.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      Also, some patients may respond only if drugs such as aspirin or leukotriene antagonists are added, which may relate to the predominant mediator released by their mast cells on activation.
      • Butterfield J.H.
      • Weiler C.R.
      Prevention of mast cell activation disorder-associated clinical sequelae of excessive prostaglandin D(2) production.

      Mast Cell Activation Disorders: Classification and Diagnostic Approach

      With improvements in the understanding of mast cell activation disorders, it has become useful to classify them into 3 distinct categories: primary, secondary, and idiopathic, as follows
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      • Akin C.
      • Valent P.
      • Metcalfe D.D.
      Mast cell activation syndrome: proposed diagnostic criteria.
      :
      Primary
      • Cutaneous mastocytosis (urticaria pigmentosa, diffuse, telangiectasia macularis eruptiva perstans)
      • Systemic mastocytosis (indolent, aggressive, associated with a hematologic non–mast cell lineage disease, mast cell leukemia)
      • Mast cell sarcoma
      • Mastocytoma
      • MMAS
      Secondary
      • IgE-mediated hypersensitivity reactions (eg, food, insect, drug-induced anaphylaxis)
      • Drugs (eg, vancomycin, opioids, taxanes)
      • Mast cell hyperplasia (associated with chronic infections, neoplasia, and autoimmune conditions, possibly due to an excess of stem cell factor; these reactive states are infrequently the cause of mast cell activation disorders
        • Valent P.
        • Akin C.
        • Arock M.
        • et al.
        Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
        )
      Idiopathic
      • IA
      • MCAS
      Secondary causes of mast cell activation should be sought in every patient because they may coexist with primary and idiopathic disorders.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      For instance, it is not unusual to find a history of systemic reaction to hymenoptera stings in patients with SM, MMAS, or even MCAS.
      • Bonadonna P.
      • Perbellini O.
      • Passalacqua G.
      • et al.
      Clonal mast cell disorders in patients with systemic reactions to Hymenoptera stings and increased serum tryptase levels.
      • Alvarez-Twose I.
      • Gonzalez de Olano D.
      • Sanchez-Munoz L.
      • et al.
      Clinical, biological, and molecular characteristics of clonal mast cell disorders presenting with systemic mast cell activation symptoms.
      • Alvarez-Twose I.
      • Gonzalez-de-Olano D.
      • Sanchez-Munoz L.
      • et al.
      Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
      Also, it is important to consider unusual allergens, such as alpha-gal, which causes delayed IgE-mediated reactions to mammalian meat, before concluding to an idiopathic disorder.
      • Commins S.P.
      • Platts-Mills T.A.
      Delayed anaphylaxis to red meat in patients with IgE specific for galactose alpha-1,3-galactose (alpha-gal).
      A primary mast cell disorder should be suspected in any patient presenting with a systemic reaction to hymenoptera stings or episodes of mast cell activation either without an identifiable trigger or with multiple unrelated triggers, especially if associated with hypotension and if urticaria or angioedema is absent.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      • Bonadonna P.
      • Perbellini O.
      • Passalacqua G.
      • et al.
      Clonal mast cell disorders in patients with systemic reactions to Hymenoptera stings and increased serum tryptase levels.
      • Alvarez-Twose I.
      • Gonzalez-de-Olano D.
      • Sanchez-Munoz L.
      • et al.
      Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
      • Cardet J.C.
      • Castells M.C.
      • Hamilton M.J.
      Immunology and clinical manifestations of non-clonal mast cell activation syndrome.
      As a first step, a baseline serum tryptase level should be measured because an increased level (>11.4 ng/mL) would favor the presence of a primary disorder.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      • Alvarez-Twose I.
      • Gonzalez de Olano D.
      • Sanchez-Munoz L.
      • et al.
      Clinical, biological, and molecular characteristics of clonal mast cell disorders presenting with systemic mast cell activation symptoms.
      Then, depending on the clinical features and the tryptase level, a bone marrow biopsy should be performed to allow the diagnosis of a primary mast cell disorder. A baseline tryptase level >20 ng/mL, episodes of unexplained anaphylaxis, and the presence of urticaria pigmentosa (the most common form of cutaneous mastocytosis) in adults are generally considered indications for bone marrow biopsy.
      • Cardet J.C.
      • Castells M.C.
      • Hamilton M.J.
      Immunology and clinical manifestations of non-clonal mast cell activation syndrome.
      Also, abnormalities on complete blood count in patients with a mast cell activation disorder should lead to a bone marrow biopsy because several hematologic non–mast cell lineage disorders can be associated with SM (SM-AHNMD [SM associated with a hematologic non–mast cell lineage disease]). These patients usually have cytopenias or thrombocytosis and/or leukocytosis on complete blood count, are male, have fewer skin symptoms, and are older than patients with pure SM.
      • Wang S.A.
      • Hutchinson L.
      • Tang G.
      • et al.
      Systemic mastocytosis with associated clonal hematological non-mast cell lineage disease: clinical significance and comparison of chromosomal abnormalities in SM and AHNMD components.
      The most commonly associated hematologic diseases are chronic myelomonocytic leukemia and myelodysplastic syndrome (60%), but other myeloproliferative neoplasms and lymphoproliferative diseases have also been described.
      • Wang S.A.
      • Hutchinson L.
      • Tang G.
      • et al.
      Systemic mastocytosis with associated clonal hematological non-mast cell lineage disease: clinical significance and comparison of chromosomal abnormalities in SM and AHNMD components.
      Finally, the presence of unexplained osteoporosis, hepatomegaly, or splenomegaly in patients with a mast cell activation disorder should raise suspicion for an aggressive variant of SM and therefore justifies a bone marrow biopsy.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      SM is diagnosed, according to the following World Health Organization criteria, as the presence of either the major criterion listed subsequently and at least 1 of the 4 minor criteria, or at least 3 minor criteria if the major criterion is not met
      • Horny H.P.
      • Sotlar K.
      • Valent P.
      Evaluation of mast cell activation syndromes: impact of pathology and immunohistology.
      :
      Major criterion
      • Multifocal, dense infiltrates of mast cells (≥15 mast cells in aggregates) detected in sections of bone marrow and/or other extracutaneous organ(s)
      Minor criteria
      • In biopsy sections of bone marrow or other extracutaneous organs, >25% of the mast cells in the infiltrate are spindle-shaped or have atypical morphology, or, of all mast cells in bone marrow aspirate smears, >25% are immature or atypical
      • Detection of an activating point mutation at codon 816 of KIT in bone marrow, blood, or other extracutaneous organ
      • Mast cells in bone marrow, blood, or other extracutaneous organ express CD2 and/or CD25 in addition to normal mast cell markers
      • Serum total tryptase persistently exceeds 20 ng/mL (unless there is an associated clonal myeloid disorder, in which case this parameter is not valid)
      These criteria encompass the diverse mast cell abnormalities that are thought to result from an exon 17 KIT mutation (D816V in >90%), which drives the clonal expansion of bone marrow mast cells.
      • Horny H.P.
      • Sotlar K.
      • Valent P.
      Evaluation of mast cell activation syndromes: impact of pathology and immunohistology.
      Additionally, 4 categories of SM have been described: indolent SM (ISM), aggressive SM (ASM), SM-AHNMD, and mast cell leukemia (MCL).
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      These are usually distinguished based on bone marrow biopsy findings and associated organ involvement (eg, liver failure, hypersplenism, cytopenias, bone lesions).
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      Patients with more aggressive forms of SM (ASM and MCL) carry the D816V KIT mutation in cells from other myeloid lineages and even hematopoietic stem cells in contrast to patients with ISM or MMAS, in whom the mutation is found only in the mast cell lineage.
      • Teodosio C.
      • Garcia-Montero A.C.
      • Jara-Acevedo M.
      • et al.
      Mast cells from different molecular and prognostic subtypes of systemic mastocytosis display distinct immunophenotypes.
      MMAS is diagnosed based on the presence of clonal mast cells in the bone marrow specimens of patients who do not meet the diagnostic criteria of SM (fulfilling only 1 or 2 minor criteria).
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      Clonality is usually revealed by the presence of the D816V KIT mutation and aberrant expression of CD25 on bone marrow mast cells.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      Two independent groups first described patients with this condition in 2007,
      • Akin C.
      • Scott L.M.
      • Kocabas C.N.
      • et al.
      Demonstration of an aberrant mast-cell population with clonal markers in a subset of patients with “idiopathic” anaphylaxis.
      • Sonneck K.
      • Florian S.
      • Mullauer L.
      • et al.
      Diagnostic and subdiagnostic accumulation of mast cells in the bone marrow of patients with anaphylaxis: monoclonal mast cell activation syndrome.
      and a few more have been reported since.
      • Bonadonna P.
      • Perbellini O.
      • Passalacqua G.
      • et al.
      Clonal mast cell disorders in patients with systemic reactions to Hymenoptera stings and increased serum tryptase levels.
      • Alvarez-Twose I.
      • Gonzalez de Olano D.
      • Sanchez-Munoz L.
      • et al.
      Clinical, biological, and molecular characteristics of clonal mast cell disorders presenting with systemic mast cell activation symptoms.
      • Alvarez-Twose I.
      • Gonzalez-de-Olano D.
      • Sanchez-Munoz L.
      • et al.
      Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
      In a case reported by Sonneck et al,
      • Sonneck K.
      • Florian S.
      • Mullauer L.
      • et al.
      Diagnostic and subdiagnostic accumulation of mast cells in the bone marrow of patients with anaphylaxis: monoclonal mast cell activation syndrome.
      the patient presented with a history of systemic reaction to hymenoptera stings and had an elevated baseline serum tryptase (12 ng/mL), whereas in the case series by Akin et al,
      • Akin C.
      • Scott L.M.
      • Kocabas C.N.
      • et al.
      Demonstration of an aberrant mast-cell population with clonal markers in a subset of patients with “idiopathic” anaphylaxis.
      patients had episodes of IA. In both studies, KIT mutations could not be found on unsorted bone marrow samples, although all patients had bone marrow mast cells with an aberrant morphology (spindle shaped) and CD25 expression.
      • Akin C.
      • Scott L.M.
      • Kocabas C.N.
      • et al.
      Demonstration of an aberrant mast-cell population with clonal markers in a subset of patients with “idiopathic” anaphylaxis.
      • Sonneck K.
      • Florian S.
      • Mullauer L.
      • et al.
      Diagnostic and subdiagnostic accumulation of mast cells in the bone marrow of patients with anaphylaxis: monoclonal mast cell activation syndrome.
      In 2009, Bonadonna et al
      • Bonadonna P.
      • Perbellini O.
      • Passalacqua G.
      • et al.
      Clonal mast cell disorders in patients with systemic reactions to Hymenoptera stings and increased serum tryptase levels.
      reported 9 patients with MMAS diagnosed following a systemic reaction to hymenoptera stings and the finding of elevated baseline serum tryptase. Two patients had the D816V KIT mutation, 1 had a D816H KIT mutation, and no mutations were found in the remainder.
      • Bonadonna P.
      • Perbellini O.
      • Passalacqua G.
      • et al.
      Clonal mast cell disorders in patients with systemic reactions to Hymenoptera stings and increased serum tryptase levels.
      Also, in 2 patients with a KIT mutation, aberrant CD25 expression was not detected.
      • Bonadonna P.
      • Perbellini O.
      • Passalacqua G.
      • et al.
      Clonal mast cell disorders in patients with systemic reactions to Hymenoptera stings and increased serum tryptase levels.
      Alvarez-Twose et al
      • Alvarez-Twose I.
      • Gonzalez de Olano D.
      • Sanchez-Munoz L.
      • et al.
      Clinical, biological, and molecular characteristics of clonal mast cell disorders presenting with systemic mast cell activation symptoms.
      mentioned 3 patients with MMAS (with a KIT mutation and aberrant CD25 expression) in a 2010 study, although patients with aberrant CD25 expression in the absence of a KIT mutation or vice versa were excluded. In 2012, Alvarez-Twose et al
      • Alvarez-Twose I.
      • Gonzalez-de-Olano D.
      • Sanchez-Munoz L.
      • et al.
      Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
      reported 11 patients with KIT mutations in bone marrow mast cells, and only 4 of those had aberrant CD25 expression. Almost half of cases (45.5%) had a history of systemic reaction to hymenoptera stings and 54.5% had an episode of syncope. Given the rarity of this syndrome and the bone marrow mast cell–enrichment techniques often necessary for its diagnosis (due to the low number of abnormal mast cells), referral of patients in whom this condition is suspected to centers with expertise in mastocytosis is strongly encouraged.
      Cutaneous mastocytosis (CM) is a primary mast cell disorder in which the skin is the only organ affected by abnormal mast cells that have been found to also carry KIT mutations.
      • Bodemer C.
      • Hermine O.
      • Palmerini F.
      • et al.
      Pediatric mastocytosis is a clonal disease associated with D816V and other activating c-KIT mutations.
      Several forms of cutaneous disease have been described, but urticaria pigmentosa is by far the most common.
      • Castells M.
      • Metcalfe D.D.
      • Escribano L.
      Diagnosis and treatment of cutaneous mastocytosis in children: practical recommendations.
      In children, cutaneous mastocytosis is rarely associated with systemic disease and therefore a bone marrow biopsy is unwarranted.
      • Castells M.
      • Metcalfe D.D.
      • Escribano L.
      Diagnosis and treatment of cutaneous mastocytosis in children: practical recommendations.
      Importantly, despite the absence of systemic disease, the local release of mediators from skin mast cells is sufficient to cause systemic symptoms of mediator release, and such an occurrence should not be misinterpreted as a sign of systemic disease.
      • Castells M.
      • Metcalfe D.D.
      • Escribano L.
      Diagnosis and treatment of cutaneous mastocytosis in children: practical recommendations.
      Also, the vast majority of children will undergo spontaneous resolution of CM before puberty, although in a cohort of 50 children with CM, 42% carried an exon 17 KIT mutation.
      • Bodemer C.
      • Hermine O.
      • Palmerini F.
      • et al.
      Pediatric mastocytosis is a clonal disease associated with D816V and other activating c-KIT mutations.
      • Castells M.
      • Metcalfe D.D.
      • Escribano L.
      Diagnosis and treatment of cutaneous mastocytosis in children: practical recommendations.
      In contrast, most adults with CM have an underlying SM and should undergo a bone marrow biopsy regardless of the presence of associated systemic symptoms of mediator release.
      • Cardet J.C.
      • Castells M.C.
      • Hamilton M.J.
      Immunology and clinical manifestations of non-clonal mast cell activation syndrome.
      Conversely, 80% of SM patients have cutaneous disease that manifests as urticaria pigmentosa.
      • Akin C.
      • Valent P.
      • Metcalfe D.D.
      Mast cell activation syndrome: proposed diagnostic criteria.
      In contrast, patients with MMAS and MCAS never have CM, and patients with ASM or MCL frequently lack CM.
      • Pardanani A.
      Systemic mastocytosis: disease overview, pathogenesis, and treatment.
      Finally, there remains a category of patients in whom no mast cell abnormality can be identified and no secondary cause can be found to account for their episodes of mast cell activation. This disorder has been termed MCAS, and its diagnostic criteria include those of any mast cell activation disorder with the additional requirement that primary, secondary, and other well-defined idiopathic mast cell activation disorders be ruled out first.
      • Akin C.
      • Valent P.
      • Metcalfe D.D.
      Mast cell activation syndrome: proposed diagnostic criteria.
      Importantly, these patients should not meet the diagnostic criteria for IA although they might experience IA from time to time. In that case, these patients should be referred to as MCAS with IA.
      • Akin C.
      • Valent P.
      • Metcalfe D.D.
      Mast cell activation syndrome: proposed diagnostic criteria.
      • Cardet J.C.
      • Castells M.C.
      • Hamilton M.J.
      Immunology and clinical manifestations of non-clonal mast cell activation syndrome.
      Alvarez-Twose et al
      • Alvarez-Twose I.
      • Gonzalez de Olano D.
      • Sanchez-Munoz L.
      • et al.
      Clinical, biological, and molecular characteristics of clonal mast cell disorders presenting with systemic mast cell activation symptoms.
      described 32 patients with this syndrome in 2010, of whom 69% were women. They were compared with a cohort of 48 patients with ISM without cutaneous disease. It was found that a higher baseline serum tryptase (>25 ng/mL), male sex, the presence of hypotensive episodes, and the absence of urticaria and angioedema favored a clonal mast cell disorder (eg, ISM).
      • Alvarez-Twose I.
      • Gonzalez de Olano D.
      • Sanchez-Munoz L.
      • et al.
      Clinical, biological, and molecular characteristics of clonal mast cell disorders presenting with systemic mast cell activation symptoms.
      A clinical score derived from these characteristics was validated in another study in which it was found to be a more accurate predictor of clonal mast cell disorder compared with baseline serum tryptase level alone.
      • Alvarez-Twose I.
      • Gonzalez-de-Olano D.
      • Sanchez-Munoz L.
      • et al.
      Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
      In 2011, Hamilton et al
      • Hamilton M.J.
      • Hornick J.L.
      • Akin C.
      • et al.
      Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
      reported on 18 patients with MCAS, of whom 16 were women. Their most common symptom was abdominal pain, a minority (17%) had had anaphylaxis, and their mean baseline serum tryptase was 10.7 ng/mL, providing support for the differentiating clinical characteristics proposed by Alvarez-Twose et al.
      • Alvarez-Twose I.
      • Gonzalez de Olano D.
      • Sanchez-Munoz L.
      • et al.
      Clinical, biological, and molecular characteristics of clonal mast cell disorders presenting with systemic mast cell activation symptoms.
      Table III delineates the distinctive features of SM, MMAS, MCAS, and IA, and the Figure provides a diagnostic algorithm to mast cell activation disorders.
      Table IIIComparison of SM, MMAS, MCAS, and IA.
      Clinical and Laboratory FeaturesSMMMASMCASIA
      Multifocal mast cell aggregatesPresent
      Major diagnostic criterion for SM; not present in all patients with SM.
      AbsentAbsentAbsent
      D816V KIT mutationPresent
      Other KIT mutations have also been associated with SM.
      Present
      May require enrichment of bone marrow mast cells.
      AbsentAbsent
      Aberrant CD25 expression on bone marrow mast cellsPresentPresent
      May require enrichment of bone marrow mast cells.
      AbsentAbsent
      Baseline tryptaseElevated
      Serum tryptase >20 ng/mL is a minor criterion for SM; not present in all patients with SM.
      Normal or elevatedNormal or elevatedNormal
      Baseline 24-hour urine methylhistamine or Prostaglandin D2/11β-PGFElevatedNormal or elevatedNormal or elevatedNormal
      Urticaria pigmentosaPresent or absentAbsentAbsentAbsent
      Mediator release symptomsPresentPresentPresentPresent
      Response to antimediator therapyGoodGoodGoodVariable
      Adapted with permission from J Allergy Clin Immunol.
      • Akin C.
      • Valent P.
      • Metcalfe D.D.
      Mast cell activation syndrome: proposed diagnostic criteria.
      IA = idiopathic anaphylaxis; MCAS = idiopathic mast cell activation syndrome; MMAS = monoclonal mast cell activation syndrome; PGF = platelet-derived growth factor; SM = systemic mastocytosis.
      low asterisk Major diagnostic criterion for SM; not present in all patients with SM.
      Other KIT mutations have also been associated with SM.
      May require enrichment of bone marrow mast cells.
      § Serum tryptase >20 ng/mL is a minor criterion for SM; not present in all patients with SM.
      Figure thumbnail gr1
      FigureDiagnostic algorithm for mast cell activation disorders. AHNMD = associated hematologic non–mast cell lineage disease; MCA = mast cell activation; MCAD = mast cell activation disorder; MCAS = mast cell activation syndrome; MMAS = monoclonal mast cell activation syndrome; SM = systemic mastocytosis.

      Treatment of MMAS and MCAS

      Treatment of patients with MMAS and MCAS is aimed at mitigating the effects of mediators released by mast cells on activation and to a certain extent at preventing mediator release. Unfortunately, no curative therapy exists for these conditions at the present time. Therefore, the aim of treatment is to achieve symptom control so as to normalize quality of life. Few patient cohorts with these diseases have been described to date and thus the prophylactic treatment regimen is largely based on the one used in patients with SM for which a larger body of evidence is available.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      The treatment approach is stepwise, usually starting with a combination of H1-receptor and H2-receptor blockers, with adjustments according to symptoms and response to treatment (Table IV). In patients with MCAS the rate of response to antimediator therapy is rather good, with 33% showing complete response, 33% a major response, and 33% a minor response after 1 year of treatment.
      • Hamilton M.J.
      • Hornick J.L.
      • Akin C.
      • et al.
      Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
      Also, symptoms may not be equally responsive to treatment, as shown in Table V.
      • Hamilton M.J.
      • Hornick J.L.
      • Akin C.
      • et al.
      Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
      No data on the response to treatment in MMAS patients were found.
      Table IVStepwise prophylactic treatment approach for patients with MCAS and MMAS.
      System/Symptoms/Step No.Drugs
      Skin
       Pruritus, flushing, urticaria, angioedema, dermatographism
        1H1-blockers
      Nonsedating second-generation H1-blockers preferred.
      ± H2-blockers
        2Leukotriene antagonists
      Montelukast, zafirlukast, or zileuton.
        3Aspirin
      Especially useful in patients with treatment-resistant flushing and elevated urinary prostaglandin D2.
        4Ketotifen
      Gastrointestinal
       Diarrhea, abdominal cramping, nausea, vomiting
        1H2-blockers
        2Cromolyn sodium
        3Proton pomp inhibitors
        4Leukotriene antagonists
      Montelukast, zafirlukast, or zileuton.
        5Ketotifen
      Neurologic
       Headache, poor concentration and memory, brain fog
        1H1- and H2-blockers
        2Cromolyn sodium
        3Ketotifen
      Cardiovascular
       Pre-syncope, syncope, tachycardia
        1H1- and H2-blockers
        2Corticosteroids
      Suggested initial dose of 0.5 mg/kg/d tapered over 1 to 3 months.
        3Omalizumab
      For recurrent anaphylactic episodes (≥1/mo) unresponsive to corticosteroids or dependent on corticosteroids for control.
      Pulmonary
       Wheezing, throat swelling
        1H1- and H2-blockers
        2Leukotriene antagonists
      Montelukast, zafirlukast, or zileuton.
        3Corticosteroids (including inhaled corticosteroids)
      Suggested initial dose of 0.5 mg/kg/d tapered over 1 to 3 months.
        4Omalizumab
      For recurrent anaphylactic episodes (≥1/mo) unresponsive to corticosteroids or dependent on corticosteroids for control.
      Anaphylaxis
       AcuteEpinephrine (intramuscular)
        1H1- and H2-blockers
        2Corticosteroids
      Suggested initial dose of 0.5 mg/kg/d tapered over 1 to 3 months.
        3Omalizumab
      For recurrent anaphylactic episodes (≥1/mo) unresponsive to corticosteroids or dependent on corticosteroids for control.
      Naso-ocular
       Nasal stuffiness, nasal pruritus, conjunctival injection
        1H1-blockers (including topical formulations)
        2Topical corticosteroids
        3Cromolyn sodium (topical formulation)
      low asterisk Nonsedating second-generation H1-blockers preferred.
      Montelukast, zafirlukast, or zileuton.
      Especially useful in patients with treatment-resistant flushing and elevated urinary prostaglandin D2.
      § Suggested initial dose of 0.5 mg/kg/d tapered over 1 to 3 months.
      For recurrent anaphylactic episodes (≥1/mo) unresponsive to corticosteroids or dependent on corticosteroids for control.
      Table VResponse to treatment in MCAS patients.
      SymptomResponse Rate, %
      Abdominal pain82
      Headache80
      Diarrhea75
      Poor concentration and memory58
      Flushing38
      Created with data from reference
      • Hamilton M.J.
      • Hornick J.L.
      • Akin C.
      • et al.
      Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
      .

      Trigger Avoidance

      Identification and avoidance of relevant triggers of mast cell activation in a particular patient is of prime importance for symptom control:
      • Alcohol (estimated prevalence in MCAS patients, 67%
        • Hamilton M.J.
        • Hornick J.L.
        • Akin C.
        • et al.
        Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
        )
      • Heat (estimated prevalence in MCAS patients, 50%
        • Hamilton M.J.
        • Hornick J.L.
        • Akin C.
        • et al.
        Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
        )
      • Drugs (estimated prevalences in MCAS and MMAS patients, 30.8% and 36.4%, respectively
        • Alvarez-Twose I.
        • Gonzalez-de-Olano D.
        • Sanchez-Munoz L.
        • et al.
        Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
        )
      •  Antibiotics
      •  NSAIDs
      •  Narcotics
      •  Neuromuscular blocking agents
      • Radiocontrast media
      • Invasive procedures (eg, general anesthesia, biopsy, endoscopy)
      • Hymenoptera stings (estimated prevalences in MCAS and MMAS patients, 21.2% and 45.5%9)
      • Fever or infection
      • Exercise
      • Physical stimuli (eg, pressure, friction)
      • Emotions/stress
      • NSAIDs
      In patients with MCAS, alcohol and heat are the most common triggers of symptoms.
      • Hamilton M.J.
      • Hornick J.L.
      • Akin C.
      • et al.
      Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
      Hymenoptera stings are also frequently reported as triggers in MMAS and MCAS and, importantly, can be the sole manifestation of the disease.
      • Alvarez-Twose I.
      • Gonzalez-de-Olano D.
      • Sanchez-Munoz L.
      • et al.
      Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
      Those patients should be thoroughly investigated for the presence of venom-specific IgEs and if present should be offered venom immunotherapy (VIT).
      • Bonadonna P.
      • Perbellini O.
      • Passalacqua G.
      • et al.
      Clonal mast cell disorders in patients with systemic reactions to Hymenoptera stings and increased serum tryptase levels.
      • Alvarez-Twose I.
      • Gonzalez-de-Olano D.
      • Sanchez-Munoz L.
      • et al.
      Validation of the REMA score for predicting mast cell clonality and systemic mastocytosis in patients with systemic mast cell activation symptoms.
      • Gonzalez-de-Olano D.
      • Alvarez-Twose I.
      • Vega A.
      • et al.
      Venom immunotherapy in patients with mastocytosis and hymenoptera venom anaphylaxis.
      • Bonadonna P.
      • Zanotti R.
      • Muller U.
      Mastocytosis and insect venom allergy.
      Indeed, patients with clonal mast cell disorders, mainly SM, and hymenoptera venom allergy are at high risk for anaphylaxis from a recurrent sting, and VIT has been shown to reduce that risk to ∼25%.
      • Gonzalez de Olano D.
      • Alvarez-Twose I.
      • Esteban-Lopez M.I.
      • et al.
      Safety and effectiveness of immunotherapy in patients with indolent systemic mastocytosis presenting with Hymenoptera venom anaphylaxis.
      However, the buildup phase of VIT can also induce systemic reactions, particularly in patients with elevated baseline serum tryptase concentration.
      • Gonzalez de Olano D.
      • Alvarez-Twose I.
      • Esteban-Lopez M.I.
      • et al.
      Safety and effectiveness of immunotherapy in patients with indolent systemic mastocytosis presenting with Hymenoptera venom anaphylaxis.
      • Bonadonna P.
      • Zanotti R.
      • Caruso B.
      • et al.
      Allergen specific immunotherapy is safe and effective in patients with systemic mastocytosis and Hymenoptera allergy.
      Therefore, it should be done under close supervision and under the cover of premedication with antihistamines and, in some cases, omalizumab.
      • Bonadonna P.
      • Zanotti R.
      • Muller U.
      Mastocytosis and insect venom allergy.
      • Kontou-Fili K.
      High omalizumab dose controls recurrent reactions to venom immunotherapy in indolent systemic mastocytosis.
      Finally, as patient fatalities have been reported following discontinuation of VIT after the usual 3- to 5-year duration, it is now recommended to give VIT for the patient's lifetime in those with an elevated baseline serum tryptase level.
      • Bonadonna P.
      • Zanotti R.
      • Muller U.
      Mastocytosis and insect venom allergy.
      Other preventable triggers of mast cell activation include invasive medical procedures, such as general anesthesia and radiologic procedures with contrast media.
      • Cardet J.C.
      • Castells M.C.
      • Hamilton M.J.
      Immunology and clinical manifestations of non-clonal mast cell activation syndrome.
      Premedication is usually recommended in patients with SM and consists of H1- and H2-blockers, to which leukotriene antagonists and corticosteroids can be added, depending on the severity of the underlying disorder and previous reactions to such triggers.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      Although data are lacking and few patients with MMAS and MCAS seem to experience adverse outcomes with those interventions, it is practice to use premedication in those patients as well.
      • Brockow K.
      • Bonadonna P.
      Drug allergy in mast cell disease.

      Treatment of Acute Episodes

      Patients with MCAS and MMAS and a history of anaphylaxis and those with an elevated baseline serum tryptase concentration (>11.4 ng/mL) should carry 2 doses of epinephrine in autoinjectors at all times because mast cell mediator release is unpredictable and could be life-threatening.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      • Turk J.
      • Oates J.A.
      • Roberts 2nd, L.J.
      Intervention with epinephrine in hypotension associated with mastocytosis.
      • Akin C.
      Anaphylaxis and mast cell disease: what is the risk?.
      Epinephrine should be administered without delay intramuscularly in the thigh, with the patient in the recumbent position, in the context of an episode of mediator release with associated hypotension or respiratory compromise.
      • Lieberman P.
      • Nicklas R.A.
      • Oppenheimer J.
      • et al.
      The diagnosis and management of anaphylaxis practice parameter: 2010 update.
      Fluid resuscitation is also important in patients with anaphylaxis.
      • Lieberman P.
      • Nicklas R.A.
      • Oppenheimer J.
      • et al.
      The diagnosis and management of anaphylaxis practice parameter: 2010 update.
      Other symptoms are usually managed with H1- and H2-blockers, and β-agonists may also be necessary for treating bronchospasm, although none of these treatments should be used as a substitute for epinephrine in the event of anaphylaxis.
      • Lieberman P.
      • Nicklas R.A.
      • Oppenheimer J.
      • et al.
      The diagnosis and management of anaphylaxis practice parameter: 2010 update.
      Corticosteroids (0.5–1 mg/kg) should be considered to prevent delayed and recurrent symptoms of anaphylaxis.
      • Lieberman P.
      • Nicklas R.A.
      • Oppenheimer J.
      • et al.
      The diagnosis and management of anaphylaxis practice parameter: 2010 update.

      Prophylaxis

      Antihistamines

      Histamine is involved in a wide array of mast cell activation manifestations, and its blockade is thus of prime importance for adequate symptom control.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      Histamine exerts its effects through 4 different receptors, although H1- and H2-receptors seem to be the most relevant ones in patients with mast cell activation disorders.
      • Simons F.E.
      Advances in H1-antihistamines.
      Therefore, the use of H1- and H2-blockers is considered the starting point in any patient with MMAS or MCAS.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      • Hamilton M.J.
      • Hornick J.L.
      • Akin C.
      • et al.
      Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
      • Cardet J.C.
      • Castells M.C.
      • Hamilton M.J.
      Immunology and clinical manifestations of non-clonal mast cell activation syndrome.
      H1-blockers have been shown to be effective in controlling skin symptoms, tachycardia, and abdominal cramping in SM.
      • Worobec A.S.
      Treatment of systemic mast cell disorders.
      • Kettelhut B.V.
      • Berkebile C.
      • Bradley D.
      • Metcalfe D.D.
      A double-blind, placebo-controlled, crossover trial of ketotifen versus hydroxyzine in the treatment of pediatric mastocytosis.
      Nonsedating H1-blockers (cetirizine, fexofenadine) are preferred over older sedating ones (diphenhydramine, hydroxyzine, doxepin).
      • Worobec A.S.
      Treatment of systemic mast cell disorders.
      The dose of these agents can be doubled to achieve symptom control similar to what is done in patients with chronic urticaria.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      • Hamilton M.J.
      • Hornick J.L.
      • Akin C.
      • et al.
      Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
      • Cardet J.C.
      • Castells M.C.
      • Hamilton M.J.
      Immunology and clinical manifestations of non-clonal mast cell activation syndrome.
      • Worobec A.S.
      Treatment of systemic mast cell disorders.
      In the same manner, a combination of H1-blockers can also be used, although side effects should be monitored.
      • Worobec A.S.
      Treatment of systemic mast cell disorders.
      Ketotifen (available in Europe and Canada), which, in addition to acting as an H1-blocker, has mast cell–stabilizing properties can also be used; it is mainly effective against skin symptoms in SM.
      • Worobec A.S.
      Treatment of systemic mast cell disorders.
      • Czarnetzki B.M.
      A double-blind cross-over study of the effect of ketotifen in urticaria pigmentosa.
      • Povoa P.
      • Ducla-Soares J.
      • Fernandes A.
      • Palma-Carlos A.G.
      A case of systemic mastocytosis; therapeutic efficacy of ketotifen.
      H2-blockers are often added to H1-blockers to optimize symptom control.
      • Castells M.
      • Metcalfe D.D.
      • Escribano L.
      Diagnosis and treatment of cutaneous mastocytosis in children: practical recommendations.
      • Worobec A.S.
      Treatment of systemic mast cell disorders.
      • Gasior-Chrzan B.
      • Falk E.S.
      Systemic mastocytosis treated with histamine H1 and H2 receptor antagonists.
      • Frieri M.
      • Alling D.W.
      • Metcalfe D.D.
      Comparison of the therapeutic efficacy of cromolyn sodium with that of combined chlorpheniramine and cimetidine in systemic mastocytosis Results of a double-blind clinical trial.
      • Johnson G.J.
      • Silvis S.E.
      • Roitman B.
      • et al.
      Long-term treatment of systemic mastocytosis with histamine H2 receptor antagonists.
      In addition, H2-blockers are used to block the gastric hypersecretion found in patients with mast cell activation disorders and to relieve the associated GI symptoms.
      • Johnson G.J.
      • Silvis S.E.
      • Roitman B.
      • et al.
      Long-term treatment of systemic mastocytosis with histamine H2 receptor antagonists.
      • Hirschowitz B.I.
      • Groarke J.F.
      Effect of cimetidine on gastric hypersecretion and diarrhea in systemic mastocytosis.
      Proton pump inhibitors are also useful in treating refractory GI symptoms.
      • Worobec A.S.
      Treatment of systemic mast cell disorders.
      Oral cromolyn sodium has been shown in small placebo-controlled trials to be particularly useful in the control of GI symptoms in SM,
      • Frieri M.
      • Alling D.W.
      • Metcalfe D.D.
      Comparison of the therapeutic efficacy of cromolyn sodium with that of combined chlorpheniramine and cimetidine in systemic mastocytosis Results of a double-blind clinical trial.
      • Soter N.A.
      • Austen K.F.
      • Wasserman S.I.
      Oral disodium cromoglycate in the treatment of systemic mastocytosis.
      • Horan R.F.
      • Sheffer A.L.
      • Austen K.F.
      Cromolyn sodium in the management of systemic mastocytosis.
      and its efficacy has also been shown for neurologic (“mixed organic brain syndrome”) and skin symptoms in some patients with SM.
      • Soter N.A.
      • Austen K.F.
      • Wasserman S.I.
      Oral disodium cromoglycate in the treatment of systemic mastocytosis.
      Its mechanism of action could involve the inhibition of mast cell mediator release, although cromolyn has been found to be a weak inhibitor in that regard and to have no inhibitory effect on skin mast cells.
      • Okayama Y.
      • Benyon R.C.
      • Rees P.H.
      • et al.
      Inhibition profiles of sodium cromoglycate and nedocromil sodium on mediator release from mast cells of human skin, lung, tonsil, adenoid and intestine.
      • Weng Z.
      • Zhang B.
      • Asadi S.
      • et al.
      Quercetin is more effective than cromolyn in blocking human mast cell cytokine release and inhibits contact dermatitis and photosensitivity in humans.
      Recent data suggest that its effect on pruritus might be mediated by the inhibition of C-fiber sensory nerves rather than through mast cell inhibition.
      • Vieira Dos Santos R.
      • Magerl M.
      • Martus P.
      • et al.
      Topical sodium cromoglicate relieves allergen- and histamine-induced dermal pruritus.

      Leukotriene Antagonists

      Because cysteinyl leukotrienes mediate many signs and symptoms of mast cell activation, their blockade could in theory be beneficial. Indeed, case reports have shown a positive impact of the cysteinyl leukotriene 1 receptor blocker montelukast on wheezing and on GI and skin symptoms in pediatric patients with mastocytosis.
      • Tolar J.
      • Tope W.D.
      • Neglia J.P.
      Leukotriene-receptor inhibition for the treatment of systemic mastocytosis.
      • Turner P.J.
      • Kemp A.S.
      • Rogers M.
      • Mehr S.
      Refractory symptoms successfully treated with leukotriene inhibition in a child with systemic mastocytosis.
      • Sancho-Chust J.N.
      • Chiner E.
      • Camarasa A.
      • Llombart M.
      Recent-onset bronchial asthma as a manifestation of systemic mastocytosis.
      These patients had refractory symptoms despite treatment with H1- and H2-blockers, cromolyn sodium, and corticosteroids.
      • Tolar J.
      • Tope W.D.
      • Neglia J.P.
      Leukotriene-receptor inhibition for the treatment of systemic mastocytosis.
      • Turner P.J.
      • Kemp A.S.
      • Rogers M.
      • Mehr S.
      Refractory symptoms successfully treated with leukotriene inhibition in a child with systemic mastocytosis.
      Montelukast helped to reduce the corticosteroid dose in 1 case.
      • Tolar J.
      • Tope W.D.
      • Neglia J.P.
      Leukotriene-receptor inhibition for the treatment of systemic mastocytosis.

      Aspirin

      Prostaglandins are overproduced in many patients with mastocytosis and also in patients with MMAS and MCAS.
      • Valent P.
      • Akin C.
      • Arock M.
      • et al.
      Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.
      • Hamilton M.J.
      • Hornick J.L.
      • Akin C.
      • et al.
      Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.
      • Butterfield J.H.
      • Weiler C.R.
      Prevention of mast cell activation disorder-associated clinical sequelae of excessive prostaglandin D(2) production.
      Therefore, by using the NSAID aspirin, which inhibits cyclooxygenase, prostaglandin generation could in theory be decreased, which would in turn lead to symptom improvement.
      • Worobec A.S.
      Treatment of systemic mast cell disorders.
      However, whereas some patients benefit from this therapy, especially for refractory flushing, some experience hypersensitivity reactions.
      • Butterfield J.H.
      • Weiler C.R.
      Prevention of mast cell activation disorder-associated clinical sequelae of excessive prostaglandin D(2) production.
      • Butterfield J.H.
      • Kao P.C.
      • Klee G.C.
      • Yocum M.W.
      Aspirin idiosyncrasy in systemic mast cell disease: a new look at mediator release during aspirin desensitization.
      • Lorcerie B.
      • Arveux I.
      • Chauffert B.
      • et al.
      Aspirin and systemic mastocytosis.
      Therefore, before giving aspirin to a patient with MMAS or MCAS, a drug challenge should be performed to ensure tolerance unless the patient has a recent record of tolerating NSAIDs.
      • Worobec A.S.
      Treatment of systemic mast cell disorders.
      Butterfield et al
      • Butterfield J.H.
      • Weiler C.R.
      Prevention of mast cell activation disorder-associated clinical sequelae of excessive prostaglandin D(2) production.
      described 4 patients with a likely diagnosis of MCAS characterized by overproduction of prostaglandins but not histamine. Interestingly, they all responded well to treatment with aspirin, whereas they were all refractory to antihistamines.

      Omalizumab

      Omalizumab, a humanized monoclonal antibody that binds free IgE, has been used with success in several cases of mast cell activation disorders refractory to maximal antihistamine doses and requiring corticosteroids for symptom control.
      • Bell M.C.
      • Jackson D.J.
      Prevention of anaphylaxis related to mast cell activation syndrome with omalizumab.
      • Molderings G.J.
      • Raithel M.
      • Kratz F.
      • et al.
      Omalizumab treatment of systemic mast cell activation disease: experiences from four cases.
      Those patients also experienced recurrent episodes of anaphylaxis. With omalizumab treatment, patients showed a marked reduction in symptoms and anaphylactic episodes, allowing a reduction in concurrent medication use.
      • Bell M.C.
      • Jackson D.J.
      Prevention of anaphylaxis related to mast cell activation syndrome with omalizumab.
      • Molderings G.J.
      • Raithel M.
      • Kratz F.
      • et al.
      Omalizumab treatment of systemic mast cell activation disease: experiences from four cases.
      Effect seemed to manifest after ∼6 months of treatment and was likely related to the mast cell–stabilizing properties of omalizumab.
      • Molderings G.J.
      • Raithel M.
      • Kratz F.
      • et al.
      Omalizumab treatment of systemic mast cell activation disease: experiences from four cases.
      • Chang T.W.
      • Shiung Y.Y.
      Anti-IgE as a mast cell-stabilizing therapeutic agent.
      To the contrary, in another patient, mast cell activation symptoms followed the injections of omalizumab and led to its withdrawal.
      • Molderings G.J.
      • Raithel M.
      • Kratz F.
      • et al.
      Omalizumab treatment of systemic mast cell activation disease: experiences from four cases.
      In the same report, 2 cases of SM also showed benefit with omalizumab in symptoms and medication use.
      • Molderings G.J.
      • Raithel M.
      • Kratz F.
      • et al.
      Omalizumab treatment of systemic mast cell activation disease: experiences from four cases.

      Other Therapies

      MCAS and MMAS are benign diseases and therefore those patients are not candidates for treatment with tyrosine kinase inhibitors (TKIs) or cytoreductive therapies used in patients with smoldering ISM, ASM, or MCL.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      • Cardet J.C.
      • Castells M.C.
      • Hamilton M.J.
      Immunology and clinical manifestations of non-clonal mast cell activation syndrome.
      However, because patients with MMAS have a clonal mast cell disorder, they need to be monitored for the development of complications associated with advanced forms of SM, such as osteoporosis, bone lesions, hepatomegaly, splenomegaly, and cytopenias.
      • Valent P.
      • Akin C.
      • Escribano L.
      • et al.
      Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria.
      TKIs are a promising drug class for the treatment of patients with advanced forms of SM because they specifically target KIT.
      • Verstovsek S.
      Advanced systemic mastocytosis: the impact of KIT mutations in diagnosis, treatment, and progression.
      However, most TKIs, including imatinib, are ineffective against the D816V KIT mutation, which affects >90% of patients with SM.
      • Verstovsek S.
      Advanced systemic mastocytosis: the impact of KIT mutations in diagnosis, treatment, and progression.
      Nonetheless, a newer TKI, midostaurin, has shown promising efficacy and tolerability results in patients with the D816V KIT mutation.
      • Verstovsek S.
      Advanced systemic mastocytosis: the impact of KIT mutations in diagnosis, treatment, and progression.
      Although investigational at the present time, TKIs could be used in the future for patients with MMAS with complications such as bone loss or recurrent anaphylaxis. New drugs are also being developed that inhibit mast cell activation. As such, quercetin, a flavonoid, has been shown to block in vitro the mast cell release of histamine, prostaglandins, leukotrienes, tryptase, and inflammatory cytokines such as interleukin-6 and tumor necrosis factor-α, although its efficacy in mast cell activation disorders remains to be validated in clinical trials.
      • Weng Z.
      • Zhang B.
      • Asadi S.
      • et al.
      Quercetin is more effective than cromolyn in blocking human mast cell cytokine release and inhibits contact dermatitis and photosensitivity in humans.
      • Kempuraj D.
      • Castellani M.L.
      • Petrarca C.
      • et al.
      Inhibitory effect of quercetin on tryptase and interleukin-6 release, and histidine decarboxylase mRNA transcription by human mast cell-1 cell line.

      Conclusions

      MMAS and MCAS are new and rare diseases for which much remains to be learned about natural evolution, prognosis, and pathophysiology. Their clinical presentation, with its wide array of unspecific signs and symptoms, requires a high degree of suspicion to avoid delays in diagnosis and treatment, which are currently fairly common. It is therefore crucial to increase awareness of these syndromes in the medical community.
      A diagnosis of mast cell activation disorder should strictly abide by the recently established diagnostic criteria, which require that the patient present typical signs and symptoms, that objective evidence of mediator release be documented, and that a response to antimediator therapy be observed. It should also be made after consideration of the relevant differential diagnosis. Differentiation between the diverse primary mast cell disorders (eg, SM, MMAS) and between secondary and idiopathic (eg, MCAS) disorders requires a certain level of expertise and, in some instances, access to techniques that are not widely available at this time. Therefore, referral to a center specialized in mast cell activation disorders is encouraged to ensure proper diagnosis and optimal treatment of these patients.
      Bone marrow biopsy is crucial to verify the presence of clonal mast cells, which indicate a primary mast cell disorder. Clonality is usually established by detection of an exon 17 KIT mutation (most commonly D816V) in bone marrow mast cells. It is also suggested by an aberrant expression of CD25 by these cells. These anomalies are found in patients with MMAS who, on the other hand, do not fulfill the diagnostic requirements for SM. In contrast, MCAS is a diagnosis of exclusion in which no mast cell anomaly or secondary disorders account for the mast cell activation disorder.
      The therapeutic approach for MMAS and MCAS, in the absence of drug efficacy trials, is largely based on symptoms and tailored to the patient's response. All patients must be carefully evaluated to determine their specific risk for anaphylaxis and the need to carry 2 epinephrine autoinjectors. Prophylactic therapy usually consists of a combination of several mediator antagonists. Also, patients with hymenoptera venom allergy should be treated with lifelong VIT. For refractory cases, the use of omalizumab has been reported to be useful and is worth considering. Finally, it is still necessary to define whether and when patients with MMAS might be candidates for TKIs, as promising as they may seem for mastocytosis.
      Research on these new syndromes is thus essential, and centers with expertise in mast cell activation disorders are key in this regard because they allow for a critical mass of these patients to be enrolled in studies while providing those patients with the most up-to-date diagnostic procedures and treatment strategies.

      Conflicts of Interest

      Mariana Castells serves as consultant on adverse drug reactions for The sanofi-aventis Group and Merck and Co, Inc, and has received grants from the Mastocytosis Society and Ovation for the Cure . The authors have indicated that they have no other conflicts of interest with regard to the content of this article.

      Acknowledgment

      Drs. Picard, Giavina-Bianchi, Mezzano, and Castells performed the literature search and collected the data. Drs. Picard and Mezzano drafted the article and Drs. Giavina-Bianchi and Castells reviewed it. Dr. Giavini-Bianchi created Table I and Figure 1 and Dr. Picard created Table II, Table III, Table IV, Table V.

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