Table 3. Variants of mast cell activation syndrome.
| Mast cell activation syndrome (MCAS) variant | Key diagnostic variables |
|---|---|
| Primary MCAS | KIT D816V-mutated clonal MCs are found in most cases and also display CD25; also reported in cases with KIT-mutated mast cells and hereditary alpha-tryptasemiaa |
| Synonyms for KITGOF mutation-associated MCAS: Clonal MCAS | |
| Monoclonal MCAS (MMAS) | |
| (a) With cutaneous mastocytosis (CM) | CM criteria fulfilled; SM criteria not fulfilled |
| (b) With systemic mastocytosis (SM) | SM criteria fulfilled |
| (c) With only 2 minor SM criteria | Criteria to diagnose CM or SM not fulfilled |
| Secondary MCAS | Triggered by an allergen to which a subject is sensitive or to an non-IgE-dependent trigger of MC activation |
| Idiopathic MCAS | MCAS criteria are fulfilled, but no underlying reactive disease, no IgE-mediated allergy, and no monoclonal mast cells are detectablea |
GOF: gain of function.
a
In these patients, no activating KIT mutation at codon 816 is detected, and when tested, flow cytometry usually confirms the presence of CD25-negative (normal) mast cells.