Colonoscopy results showing melanosis coli are indicative of what condition?

Melanosis coli is a condition characterized by a dark pigmentation of the colonic mucosa, which is most commonly associated with chronic laxative abuse, particularly those containing anthraquinone derivatives, such as senna. The pigment is derived from the breakdown of melanin and results from the increased number of macrophages in the colonic mucosa that phagocytize this pigment, typically in response to a chemical irritant, which in this case is the laxative.

This finding on colonoscopy indicates a physiological response of the colon to the prolonged irritation or damage caused by the excessive use of laxatives, rather than being indicative of an acute or chronic inflammatory condition, malignancy, or diverticular disease, which would present differently on colonoscopy. Therefore, the presence of melanosis coli serves as a clear marker of laxative abuse.