Severe Melanosis Coli From Rhubarb Supplement

Abstract

Melanosis coli is a dark pigmentation of colonic wall that is often identified at the time of colonoscopy. We present a second reported case of melanosis coli in a patient taking rhubarb containing herbal laxative. 67-year-old Caucasian female with ulcerative proctosigmoiditis (in clinical remission), sclerosing pancreatitis, and slow transit constipation, noted to have black coloration of the whole colon during a screening colonoscopy. The pigmentation was very dense, limiting the mucosal examination on both standard and peak illumination (Figure 1, panel A/B). This was new from a colonoscopy 2 years prior. Minimal coble stoning was noted in the sigmoid colon. Mucosal biopsies confirmed diagnosis of melanosis coli and chronic colitis with focal mild activity in the sigmoid colon. Her medication list included alprazolam, ascorbic acid, dexlansoprazole, dicyclomine, omega-3 fatty acids, pancrelipase, tramadol and multivitamin and an herbal fiber supplement containing rhubarb. She stopped using rhubarb extract and repeat colonoscopy 2 years later showed complete resolution of melanosis coli (Figure 1, panel C). The cobblestoning of sigmoid colon was also resolved and no active colitis. Melanosis coli is pigmentation of colonic mucosa secondary to lipofuscin deposition in macrophages in the lamina propria. It is considered a result of increased apoptosis. Lysosomal digestion on cellular organelles forms lipofuscin granules. These granules are then taken up by the macrophages. Our patient reported taking rhubarb containing herbal laxative. Rhubarb has anthraquinones which passes unabsorbed through the small bowel and get activated in the colon, where they are converted to active forms. These in turn cause epithelial cell damage leading to altered absorption, secretion and motility. The epithelial cells damage leads to apoptosis. Melanosis coli is considered benign and is reversible on discontinuing implicating agent. Disappearance of the pigment usually occurs within a year after a patient stops taking anthraquinone but microscopic feature could take longer to clear.Figure: A/B - initial colonoscopy showing severe melanosis coli. Fig 1C - Repeat colonoscopy showing improved melanosis coli.