Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.

BACKGROUND Diagnostic criteria for mast cell (MC) activation syndrome have been recently proposed, but clinical studies to validate these criteria are lacking. OBJECTIVE We sought to determine the clinical manifestations of this newly recognized syndrome in a cohort of patients. METHODS We prospectively evaluated 18 patients seen at our institution with MC activation syndrome from 2006 to 2009. Patients enrolled had at least 4 of the signs and symptoms of abdominal pain, diarrhea, flushing, dermatographism, memory and concentration difficulties, or headache. Response to treatment with anti-MC mediator medications was assessed based on established criteria. Laboratory tests indicating MC mediator release and histopathology and immunohistochemical studies on gastrointestinal biopsy samples were performed. RESULTS Ninety-four percent of the patients had abdominal pain, 89% had dermatographism, 89% had flushing, and 72% had the constellation of all 3 symptoms. Patients additionally had headache, diarrhea, and memory and concentration difficulties. All patients had at least 1 positive laboratory test result for an increased MC mediator level. On the basis of the response to treatment criteria, 67% of the patients in the cohort had either a complete or major regression in symptoms while taking medications targeting MC mediators. There was no significant difference in the numbers of intestinal mucosal MCs between our patients and healthy control subjects. CONCLUSION MC activation syndrome might be the underlying cause of unexplained symptoms when several organ systems are involved, such as the gastrointestinal tract and the skin. It is especially important to be able to recognize the constellation of clinical features because response to anti-MC mediator medications is often excellent.