Mastocytic enterocolitis: increased mucosal mast cells in chronic intractable diarrhea.

Context: In some adult patients with chronic intractable diarrhea, the diagnosis remains elusive even after detailed evaluations, and colonic or duodenal biopsy specimens may appear unremarkable on routine hematoxylin-eosin staining.

Objectives: To assess the concentration of mast cells in colonic or duodenal biopsy specimens by immunohistochemical analysis for mast cell tryptase from patients with chronic intractable diarrhea and to evaluate their response to drugs affecting mast cell function.

Design: Mast cells per high-power field were assessed in biopsy specimens from 47 patients with chronic intractable diarrhea, from 50 control subjects, and from 63 patients with other specific diseases that cause chronic diarrhea (inflammatory bowel disease, celiac disease, collagenous colitis, and lymphocytic colitis). Patients with chronic intractable diarrhea who had more than 20 mast cells per high-power field were administered drugs affecting mast cell mediator function and release.

Results: The mean +/- SD concentration of mast cells in the 50 control subjects was 13.3 +/- 3.5 cells per high-power field; hence, patients with more than 20 mast cells per high-power field were considered to have increased mast cells. Thirty-three (70%) of 47 patients with chronic intractable diarrhea had increased mast cells, and symptoms were controlled by drug therapy in 22 (67%) of the 33 patients. No patient had systemic or cutaneous mastocytosis. No increase in mast cells was seen in patients with other common causes of chronic diarrhea.

Conclusions: In chronic intractable diarrhea, colonic or duodenal biopsy specimens may appear unremarkable on routine hematoxylin-eosin staining, but increased mast cells may be demonstrated by immunohistochemistry for mast cell tryptase, with the novel term mastocytic enterocolitis describing this condition. Similar increases in mast cells are not apparent in control populations or in patients with other specific diseases that cause chronic diarrhea. The cause of the increased mast cells remains to be elucidated.