Performing colonic mast cell counts in patients with chronic diarrhea of unknown etiology has limited diagnostic use

Context.-Mastocytic enterocolitis is a recently described entity defined by chronic diarrhea of unknown etiology and normal colon biopsy results with increased mast cells (MCs) seen on special stains. These patients may benefit from mast cell stabilizers; however, the clinical utility of MC counts remains unknown. Objective.-To determine the clinical utility of colonic MC counts on normal biopsies in patients with chronic diarrhea of unknown etiology. Design.-Blinded MC counts using a c-Kit stain were performed in 76 consecutive patients with chronic diarrhea of unknown etiology who had normal colon biopsy results and in 89 consecutive control patients presenting for screening colonoscopy. Mast cells were counted per single high-power field in the highest-density area. A t test was used to compare the counts, and receiver operating characteristic curves were generated to examine sensitive and specific cutoff values. Results.-Overall, MC counts averaged 31 MCs per high-power field in the study group versus 24 MCs per high-power field in the control group (P < .001). When stratified by location, a significant increase was seen in biopsies from the left colon only. Receiver operating characteristic analysis revealed that overall MC counts, left-sided MC counts, and the difference between rightand left-sided MC counts did not yield discriminatory cutoff values (area under the curve, 0.68, 0.74, and 0.81, respectively). Conclusions.-Mast cell counts were increased in patients with chronic diarrhea of unknown etiology, primarily in the left colon. However, receiver operating characteristic analysis demonstrates no discriminatory cutoff values. Quantitative MC stains yield little useful diagnostic information, and further studies are necessary to determine whether mastocytic enterocolitis truly represents a distinct entity.