Characteristics and outcomes of patients with pediatric‐onset non‐mastocytosis mast cell activation disorders: A CEREMAST study

Background Mast cell (MC) activation (MCA) disorders (MCAD) include diseases in which MCs excessively release mediators leading to recurrent manifestations of MCA. MCAD encompasses MCA syndrome (MCAS) which is defined by (i) documented systemic symptoms of MCA, (ii) a 20% increase in serum tryptase level from the individual's baseline plus 2 ng/mL and (iii) a symptom response to MC‐stabilizing drugs. MCAD not fulfilling mastocytosis or all MCAS criteria are referred to as MCAD not otherwise specified (MCAD‐NOS). The aim was to describe the clinical, laboratory characteristics and outcomes of the first pediatric‐onset non‐mastocytosis MCAD cohort. Methods All children with the criteria of non‐mastocytosis MCAD managed at the French National Referral Center for MCAD were included. Clinical, laboratory data, and outcomes were recorded. Results Forty‐four MCAD patients (mean age at onset: 4.3 years) were identified including 36 MCAD‐NOS and 8 idiopathic MCAS. Hereditary‐α‐tryptasemia was identified in 5/33 (15.2%) patients. The spectrum of symptoms concerned most frequently both the skin (100% of children, with urticaria, angioedema, pruritus, and/or flushing) and the gastrointestinal tract (93% patients). We identified two clinical profiles, according to the age at onset. Before 3 years of age, MCAD was associated with persistent gastrointestinal symptoms triggered by various foods (leading to a drastically limited diet), and after 3 years of age with episodic, recurrent, idiopathic, anaphylactic reactions. The administration of H1 and/or H2 antihistamines drugs +/− a leukotriene receptor antagonist resulted in a marked reduction in symptoms. Conclusion The description of the clinical profiles of pediatric‐onset non‐mastocytosis MCAD may help to avoid diagnostic delay.