Abstract
Mast cell activation syndrome (MCAS) covers a range of conditions resulting from recurrent mast cell degranulation, sometimes manifesting as anaphylaxis. It is defined by three criteria: a clinical presentation of mast cell activation (clinical criterion), an increase in tryptase levels (biological criterion), and a favourable response to treatment (treatment criterion). A new classification has been developed that includes mast cell activation disorders (MCAD) that do not strictly meet the above criteria (in particular the biological criterion). This leads to an increasing number of patients being detected, some of whom may however benefit from MCAS treatment. MCAS can be divided into primary (clonal), secondary and idiopathic forms. There are also forms that combine MCAS with mastocytosis, hereditary alpha-tryptasemia and/or allergy. This diagnosis of exclusion needs to be assessed by a specialised multidisciplinary team, to avoid over- and under-diagnosis. Moreover, patients often experience a prolonged medical journey, requiring management of the significant psychosocial and financial repercussions for the child and his family.