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Mast cell activation syndrome (MCAS) can be diagnosed in patients with recurrent, severe symptoms from mast cell (MC)-derived mediators, which are transiently increased in serum and are attenuated by mediator-targeting drugs. When KIT-mutated, clonal MC are detected in these patients, a diagnosis of primary MCAS can be made. Severe systemic reactions to hymenoptera venom (HV) represent the most common form of anaphylaxis in patients with mastocytosis. Patients with primary MCAS and HV anaphylaxis are predominantly males and do not have skin lesions in the majority of cases, and anaphylaxis is characterized by hypotension and syncope in the absence of urticaria and angioedema. A normal value of tryptase (≤11.4 ng/ml) in these patients does not exclude a diagnosis of mastocytosis. Patients with primary MCAS and HV anaphylaxis have to undergo lifelong venom immunotherapy, in order to prevent further potentially fatal severe reactions.

Clinical manifestations of mastocytosis in adults comprise signs and symptoms linked to mast cell (MC) activation, including anaphylaxis. Depending on MC burden, adults can be diagnosed with systemic mastocytosis, when the WHO criteria are fulfilled, or with other clonal MC disorders, characterized by MC mediator symptoms and demonstration of activating KIT mutations and/or expression of CD25 on MCs. There is a specific link between mastocytosis and hymenoptera venom allergy (HVA): the reported frequency of HVA in mastocytosis is 20-50 % and raises to 60-80 % in patients affected by indolent systemic mastocytosis without skin lesions. The presentation of HVA characterized by severe hypotension in the absence of urticarial or angioedema is typical in patient with an underlying MC disorder, even in the presence of normal baseline serum tryptase levels.

Background: A preferential association between systemic mastocytosis (SM) and hymenoptera allergy (HVA) has been observed. Patients with both diseases are at risk for more severe reactions, and venom immunotherapy (VIT) may represent a life-saving treatment, but the use of VIT in such patients raised concerns about its safety., Objective: We evaluated a large population of patients with SM and HVA who received VIT., Methods: This prospective study was performed in Italy and Spain. A diagnosis of SM and HVA and a VIT prescription were made according to international recommendations. The patients were carefully followed up during VIT, with special attention to field stings., Results: A total of 84 patients (70 men, 14 women; mean age 52.1 years) were included, 81% with grade IV reaction, 91% with indolent SM. No difference was seen between the Italian and Spanish patients. There were 10 adverse reactions during the induction phase: 3 with the conventional induction and 7 with the rush-modified induction, none resulted in epinephrine administration and/or hospitalization. Fifty patients had one or more field re-sting (95 episodes), none during induction. The time elapsed from starting VIT and first re-sting was 2 months to 7 years, and the number of re-stings per patient was 1-6. Of the 50 patients who were re-stung, 43 (86%) resulted in being fully protected. Seven patients had reactions, and the maintenance dose was safely increased to 200 mcg. The maintenance dose interval was not different between patients with and those without reactions at re-stings., Conclusion: VIT is well tolerated, safe, and effective in patients with SM., (Copyright © 2013 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)

Background: Systemic mastocytosis (SM) may be associated with hymenoptera allergy. In such cases, immunotherapy is a life-saving treatment, but a circumstantiated diagnosis is needed for its prescription. Patients with SM and previous reactions to stings, but with negative tests represent a diagnostic dilemma. The basophil activation test (BAT) may be helpful in refining the diagnosis., Objective: We assessed the usefulness of BAT in subpopulations of mastocytosis patients, including those with negative tests for insect allergy., Methods: Within a population of patients with mastocytosis and previous stings, we studied by BAT and augmented intradermal test (IDT) (10 µg/ml) two groups: (1) with reactions to stings and negative tests; (2) without reactions and negative tests. Basophil activation test was performed with different venoms, assessing at flow cytometry basophils' activation., Results: Sixty-three patients had mastocytosis and 52 had reactions to previous hymenoptera stings. Of them, seven proved negative to diagnostic tests. In six of seven of those patients, BAT was negative with all venoms, and in one, basophils resulted activated also with the negative control. In six patients without previous reactions and negative tests, BAT was totally negative in five of six patients and weakly positive to Hornet in one. Finally, the IDT at 10 µg/ml venom produced nonspecific positive results in most cases., Conclusion: In patients with mastocytosis, the negative results of standard tests are reliable, because BAT and IDT at higher concentration do not add useful information., (© 2012 John Wiley & Sons A/S.)

Purpose of Review: To analyse the association of systemic allergic hymenoptera sting reactions with mastocytosis and elevated baseline serum tryptase and to discuss diagnosis and treatment in patients with both diseases., Recent Findings: In recent large studies on patients with mastocytosis a much higher incidence of severe anaphylaxis following hymenoptera stings than in the normal population was documented. In patients with hymenoptera venom allergy, elevated baseline tryptase is strongly associated with severe anaphylaxis. Fatal sting reactions were reported in patients with mastocytosis, notably after stopping venom immunotherapy. During venom immunotherapy most patients with mastocytosis are protected from further sting reactions. Based on these observations immunotherapy for life is recommended for patients with mastocytosis and venom allergy. The incidence of allergic side-effects is increased in patients with mastocytosis and elevated baseline tryptase, especially in those allergic to Vespula venom. Premedication with antihistamines, or omalizumab in cases with recurrent severe side-effects, can be helpful., Summary: In all patients with anaphylaxis following hymenoptera stings, baseline serum tryptase should be determined. A value above 11.4 microg/l is often due to mastocytosis and indicates a high risk of very severe anaphylaxis following re-stings. Venom immunotherapy is safe and effective in this situation.

Background: Anaphylaxis after Hymenoptera stings has been reported in subjects with mastocytosis, but few data exist regarding disease prevalence in populations allergic to these insects., Objective: The incidence of clonal mast cell (MC) disorders in subjects with both systemic reactions to Hymenoptera stings and increased serum baseline tryptase (sBT) levels was assessed by using bone marrow (BM) aspirates and biopsy specimens., Methods: Subjects with a history of a systemic reaction caused by a Hymenoptera sting underwent the standard diagnostic work-up for Hymenoptera allergy, and sBT levels were measured. Subjects with an increased sBT level had BM evaluation that included histology/cytology, flow cytometry, and detection of KIT mutations., Results: Forty-four (11.6%) of 379 subjects with systemic reactions had increased sBT levels (>11.4 ng/mL), and 31 (70.5%) of these had a history of anaphylaxis. Thirty-four subjects with increased sBT levels underwent a BM analysis. Histology detected diagnostic or subdiagnostic MC infiltrates in 22 (65%) of 34 patients. Abnormal MCs were identified by means of flow cytometry and cytology in 26 (78.8%) of 33 and 20 (58.8%) of 34 subjects, respectively. A KIT mutation was detected in 17 (54.8%) of 31 subjects. The diagnosis was indolent systemic mastocytosis in 21 (61.7%) of 34 subjects and monoclonal MC activation syndrome in 9 (26.5%) of 34 subjects. All subjects with anaphylaxis had one of those 2 disorders., Conclusion: The concomitant presence of systemic reactions (especially anaphylaxis) after Hymenoptera stings and increased sBT levels strongly suggests that a BM examination is indicated for the diagnosis of clonal MC disease.

Background: The preferential association of mastocytosis with hymenoptera sting reactions is well known, but there is no data on the prevalence of clonal mast cell disorders in subjects with severe systemic reactions due to foods or drugs. Methods: Patients with food- or drug-induced severe systemic reactions, including anaphylaxis, and increased serum tryptase were studied for the presence of mastocytosis, and compared with a population of patients with hymenoptera allergy. The aetiological role of foods or drugs was assessed according to current recommendations. Systemic reactions were graded in severity according to the procedure described by Mueller. Serum tryptase was considered increased if the level was >11.4 ng/ml. Subjects with increased tryptase had dermatological evaluation and Bone marrow(BM) aspirate-biopsy, which included histology/cytology, flow cytometry and detection of KIT mutations. Results: A total of 137 subjects (57 male, mean age 42 years) were studied. Of them, 86 proved positive for drugs and 51 for foods. Overall, out of 137 patients, only nine (6.6%) had a basal tryptase >11.4 ng/ml, and only two (1.5%) were diagnosed with mastocytosis. This was clearly different from patients with hymenoptera allergy, where 13.9% had elevated tryptase and 11.1% had a clonal mast cell disorder. Conclusion: The association of clonal mast cell disorders with hymenoptera allergy seems to be more specific than that with food- or drug-induced systemic reactions. [ABSTRACT FROM AUTHOR]