Murray, J.

Background: Mastocytic enterocolitis has been proposed as a cause of chronic diarrhea and abdominal pain, characterized by increased mast cells in gastrointestinal mucosal biopsies. However, its clinical significance remains uncertain. Methods: We present a case report of a patient identified to have high levels of mast cells on gastrointestinal biopsies. We then reviewed cases at Mayo Clinic where patients had >20 mast cells per high-power field (HPF) on gastrointestinal biopsies. Patients with alternative explanations for mast cell elevation, including systemic mastocytosis were excluded. We analyzed demographics, clinical presentations, pathology reports, serum and urine mast cell mediators, inflammatory markers, bone marrow biopsies, motility testing, and treatment responses. Results: We identified 42 patients (30 female and 12 male) with elevated mast cells on biopsy (mean age: 41 y, range: 17 to 81). Mast cells were quantified using KIT (CD117) staining, with no abnormal clumping or morphology, and CD25 immunostaining was negative in all cases. Eosinophilic infiltration was absent in all but one case. Small intestinal bacterial overgrowth (SIBO) was found in 78% of patients tested. Treatments varied widely, with antihistamines and cromolyn being the most common. Among 21 patients with sufficient follow-up, only 5 (24%) reported partial or complete symptom improvement, while 76% experienced persistent symptoms. Conclusion: Routine assessment of mast cells on gastrointestinal biopsies is not supported by our findings. Elevated mucosal mast cells, in the absence of systemic mast cell disorders, may not indicate a distinct disease entity. Evaluation should focus on ruling out other inflammatory, allergic, infectious, and motility disorders, as well as SIBO. Further research is needed to determine the clinical significance of increased mucosal mast cells and their role in gastrointestinal symptomatology.