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Melanosis coli

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Melanosis coli is dark brown-black pigmentation of colorectal mucosa associated with chronic use of laxatives containing anthraquinone. Examples of such laxatives include senna and rhubarb derivatives.

Clinical Importance: There is no association between colorectal cancer and melanosis coli or laxative use. However, colorectal adenomas are found more frequently in patients with melanosis coli during endoscopy. This is due to the fact that adenomas do not contain the pigment and are readily detected as lighter spots against dark brown-black colonic mucosa. Melanosis coli is benign and reversible. The pigment disappears within about a year after the patient stops taking laxatives.

Pathology: The active ingredient anthraquinone has a direct toxic effect on colonic epithelial cells resulting in the production of lipofuscin which is taken up by the macrophages. At colonoscopy, the affected segments of colon show dark brown and black pigmentation. The changes are most prominent in cecum and rectum, although it can affect the entire large bowel. The intestinal discoloration may be diffuse or patterned (as seen here) and vary in intensity from segment to segment.

Image courtesy of: Michael Feely, DO, University of Florida, Gainesville, Florida, USA.

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