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Benign Discoloration Poses Questions
Q: What Should I Suspect When I See Melanosis Coli and What Is Its Clinical Relevance?
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Image: Roberson E, Wald A
A: Melanosis coli is a dark brown-black discoloration of the colonic mucosa most often seen with exposure to anthraquinone laxatives (Figure 1). It is usually more prominent in the proximal colon and cecum, although it can affect the entire large bowel. Up to 70% of patients who use anthraquinone laxatives chronically will develop melanosis coli within 4 to 12 months of starting the drug. It is therefore often seen in women aged 20 to 70 (the population most often affected with constipation), but its development does not depend on age or duration of constipation. Anthraquinone laxatives encompass cascara sagrada, senna, aloe, rhubarb, and frangula. Senna is the only anthraquinone approved by the Food and Drug Administration. The others are plant substances that may be found in products sold in homeopathic and nutritional stores. Melanosis coli has also been described uncommonly with other conditions including inflammatory bowel disease and diverticulosis and with medications including bisacodyl, topical anthralin, and bamboo leaf oil.
Melanosis coli is more accurately called pseudomelanosis coli since it is actually associated with lipofuscin, which is not melanin or a melanin-like substance. Lipofuscin is a marker for colonic epithelial cell apoptosis. Anthraquinone-containing laxatives are converted to active compounds by colonic bacteria, which induce apoptosis of colon epithelial cells. Cell remnants are then ingested by macrophages that migrate to the lamina propria where lysosymes convert remnants of cells into residual bodies containing the black pigment lipofuscin.
In a patient who complains of chronic diarrhea, melanosis coli observed on colonoscopy is virtually diagnostic for surreptitious anthraquinone laxative use (factitious diarrhea). This could be deliberate or accidental through the use of over-the-counter supplements that contain anthraquinones. Melanosis coli is benign and reversible; stopping the offending agent results in resolution within 4 to 12 months. There is no relationship between melanosis coli and colon cancer. In fact, neoplasms often can be identified more easily as they are nonpigmented and highlighted against the diffusely pigmented background. There is no evidence that melanosis coli causes changes in colonic motility or secretion or that it has any physiologic importance.
Excerpted from:
Cash BD, Farraye FA, eds. Curbside Consultation of the Colon: 49 Clinical Questions, Second Edition (pp 51-53)© 2009 SLACK Incorporated.
- References:
- Nascimbeni R, et al. Cancer Epidemiol Biomarkers Prev. 2002;11(8):753-757.
- Villanacci V, et al. Histopathology. 2006;49(2):132-137.
- Wald A. Constipation and constipation syndromes. In: Weinstein WM, Hawkey CJ, Bosch J, eds. Clinical Gastroenterology and Hepatology: Diseases of the Gut and Liver. Philadelphia, PA: Elselvier, Inc; 2005:443-452.
- For more information on the Curbside Consultation in Gastroenterology Series:
- See Healio.com/Books/Gastroenterology.