Ileal Pouch Biopsy Triggers Investigation and Diagnosis of Systemic Mastocytosis

We report a unique case of systemic mastocytosis (SM) diagnosed in an ileal pouch biopsy obtained from a 44-year-old woman with ulcerative colitis. She presented with intermittent abdominal pain and watery diarrhea that did not respond to antibiotic therapy. The pouch biopsy showed expansion of the lamina propria by aggregates of CD117 and CD25-positive abnormal mast cells. A subsequent bone marrow analysis showed an increase in abnormal mast cells. Based on World Health Organization criteria, she was diagnosed with SM and responded to cromolyn sodium therapy. Systemic mastocytosis can mimic pouchitis, and thus recognition of this condition is important for appropriate clinical management.