Clinical Approach to MCAS Diagnosis and Cutaneous Mastocytosis

Mast cell activation syndrome (MCAS) refers to conditions where inappropriate mast cell mediator release causes severe, recurrent, or systemic symptoms. MCAS was first described by Akin et al. in 2010, and the first expert consensus and classification report, known as the Vienna consensus, was published in  2012 [1, 2]. Patients must meet the full Vienna criteria  to be diagnosed with MCAS. Currently, there is no evidence to support the diagnosis of a chronic form of MCAS without the presence of severe, episodic events satisfying the aforementioned criteria [3]. 

MCAS can result from primary clonal mast cell expansion, secondary activation due to triggers, a combination of both, or be idiopathic. Combined MCAS occurs when patients have multiple mast cell-related conditions like cutaneous or systemic mastocytosis, atopy, or hereditary alpha-tryptasemia, leading to more severe symptoms (Table 1). Idiopathic MCAS is diagnosed when no primary or secondary causes are identified. Mastocytosis may not always lead to MCAS, but more widespread mast cell activation increases the risk. Table 1: Variants of MCAS