Low Prevalence of Idiopathic Mast Cell Activation Syndrome Among 703 Patients With Suspected Mast Cell Disorders

Abstract

BackgroundIdiopathic mast cell activation syndrome (iMCAS) is characterised by severe, episodic systemic mast cell (MC) activation and mediator-related symptoms, event-related increase in serum tryptase levels and response to MC-targeted therapies, in the absence of underlying IgE-mediated allergy or clonal MC disorder. Studies indicating its prevalence using evidence-based diagnostic criteria are currently lacking. ObjectiveThe present study aimed to assess prevalence, as well as clinical and laboratory features of patients with iMCAS. MethodsWe conducted a retrospective evaluation of the data from 703 consecutive patients (≥18 years old) who were referred to our centre based on suspected MC disorders. Patients underwent a thorough clinical work-up including patient history, allergy tests, KIT D816V mutation analysis and/or bone marrow investigation. Disease activity was prospectively assessed during follow-up visits. ResultsThirty-one cases with confirmed iMCAS were identified. Furthermore, hereditary alpha-tryptasemia was detected in three of the cases with baseline tryptase levels >8 ng/ml. The most common clinical presentation during the MCAS episodes was mucocutaneous symptoms in patients with iMCAS, especially urticaria/angioedema. However, these symptoms were less prevalent in clonal MCAS patients (p=0.015). The duration of diagnostic delay was significantly longer in iMCAS compared to cMCAS patients (p=0.02). ConclusionOverall prevalence of iMCAS was 4.4% in the entire cohort, which indicates that iMCAS is an uncommon condition. Screening suspected patients for the three diagnostic criteria and performing a comprehensive allergy work-up including laboratory tests and ultrasensitive mutation analysis of KIT D816V followed by applying recommended diagnostic algorithms is crucial for the diagnosis of iMCAS.