Question: A report documents a patient has been taking a rhubarb and cascara compound as a laxative for a period of 5 years. On colonoscopy the entire colon appears black and dark brown. What is the basis for this abnormal coloration of the colon?
Answer: This abnormal coloration of the colon is known as melanosis coli. The cited reference notes “the active ingredient in these substances (rhubarb and cascara) is anthraquinone, which causes injury to the colonic epithelial cells, resulting in the production of lipofuscin, the dark pigment seen in melanosis coli. The condition is benign and reversible.” (Kew ST and Chakravarthi S. Melanosis coli. 2013 NEJM 368:24)
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