MSH: A subtype of MICROSCOPIC COLITIS, characterized by chronic watery DIARRHEA of unknown origin, a normal COLONOSCOPY but abnormal histopathology on BIOPSY. Microscopic examination of biopsy samples taken from the COLON show larger-than-normal band of subepithelial COLLAGEN.,NCI: A type of microscopic colitis of unknown etiology. It is characterized by the presence of collagen deposits in the lamina propria of the colonic mucosa. Patients present with chronic watery diarrhea. Colonoscopy reveals normal-appearing mucosa. The diagnosis is made with the microscopic examination of the colonic biopsy samples.