High prevalence of anaphylaxis in patients with systemic mastocytosis - a single-centre experience.

Background: Systemic mastocytosis (SM) is a clonal mast cells disorder characterized by the proliferation, accumulation and activation of mast cells in extracutaneous tissues. The clinical picture is heterogeneous and may range from asymptomatic to potentially fatal anaphylactic reactions due to excessive mast cell mediator release.

Objective: The aim of this study was to investigate the prevalence and trigger factors of anaphylactic reactions among adult SM patients. We also explored the clinical spectrum of mast cell mediator-related symptoms in patients with SM.

Methods: This descriptive study was performed among 84 consecutive adult (≥ 18 years) patients those were diagnosed with SM according to WHO criteria. Sixty-six of the patients also underwent a comprehensive allergy work-up.

Results: Sixty of 84 patients with SM (71%) had bone marrow mast cell aggregates and fulfilled the major criteria for SM and 76 patients (91%) had indolent disease. Simultaneous occurrence of cutaneous mastocytosis was observed in 59 patients (70%). Thirty-six patients (43%) had had at least one episode of an anaphylactic reaction. The clinical courses of the reactions were usually severe and patients often presented with syncope attacks (72%). Most patients reacted after hymenoptera venom stings (19/36; 53%). In 39% (14/36), a clear aetiology could not be determined. While males and females were equally frequent among the patients with SM, anaphylaxis patients showed a male predominance (61%). Anaphylactic reactions occurred more frequently in patients without cutaneous engagement. The rate of allergy sensitization was significantly higher in SM patients with anaphylaxis as compared with non-anaphylaxis SM patients, 70% vs. 23%, respectively (P = 0.0002).

Conclusions And Clinical Relevance: Anaphylaxis is more prevalent in patients with SM, predominantly in patients with atopic SM. Hymenoptera venom-induced and idiopathic anaphylaxis were the most frequent elicitors. Our findings implicate that all mastocytosis patients with anaphylaxis should undergo detailed allergological assessment before considering treatment and preventive measures.