Clinical Approach to MCAS Diagnosis and Cutaneous Mastocytosis

Diagnosis of CM 

The diagnosis of CM is often made clinically, since Darier’s sign is pathognomonic for CM.  When there is a question, a skin biopsy with immunohistochemical staining for tryptase and KIT can be performed. Despite the widespread nature of DCM, it is usually limited to the skin. Signs  of more systemic involvement such as hepatosplenomegaly or severe systemic symptoms, or  laboratory findings such as D816V mutation in peripheral blood or a sBT > 100 mg/dL should  prompt further evaluation with bone marrow biopsy to rule out SM.  

Treatment of CM [27, 42] 

Management of CM is mainly symptomatic, and treatment is similar to that of chronic  spontaneous urticaria. Pruritus is usually controlled with non-sedating H1 anti-histamines at up to 4 times the normal daily dose. Sedating anti-histamines may be used cautiously. Leukotriene  receptor antagonists and H2-blockers can be added on if needed. Topical corticosteroids can be applied in limited CM, with close monitoring for local and systemic effects. Covering large lesions with a band-aid can reduce repeated trauma and degranulation. Epinephrine should be prescribed, and indications and technique for use reviewed, if there is a history of anaphylaxis or severe systemic symptoms, extensive skin involvement, significantly elevated sBT, and/or  concern for SM. Minimizing triggers should also be discussed, with close attention to  environmental (temperature extremes or changes, humidity), external factors (trauma, rubbing/pressure), individual factors (sleep deprivation, exercise, spicy foods, emotional stress,  infections), medications (morphine, codeine, vancomycin, NSAIDs, muscle relaxants). Other  considerations include PUVA (oral methoxypsoralen therapy with long wave psoralen plus  ultraviolet radiation) for severe forms of CM, off-label omalizumab, topical calcineurin inhibitors, oral cromolyn (especially if gastrointestinal symptoms; may also help decrease  pruritis), H2 antagonists and/or proton pump inhibitors. Rarely, surgery can be used for  mastocytoma causing significant symptoms not controllable by other treatment modalities [43].  An important part of treatment is communicating the usually benign and self-limited course of  pediatric CM [36].