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melanosis coli

Thursday 26 November 2009

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Definition: Melanosis coli, also pseudomelanosis coli, is a disorder of pigmentation of the wall of the colon, often identified at the time of colonoscopy. It is benign, and may have no significant correlation with disease. The brown pigment is lipofuscin in macrophages, not melanin. See also : melanosis

Melanosis coli has been associated with the ingestion of anthracene laxatives and is believed to be caused by increased epithelial apoptosis.

Although melanosis coli is a frequent finding in colonic biopsies and resection specimens.

Severe jet black melanosis coli with pseudoobstruction has been reported. (18269120)

Images

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Etiology

The most common cause of melanosis coli is the extended use of laxatives, and commonly anthraquinone containing laxatives such as Senna and other plant glycosides. However, other causes are identified, including an increase in colonic epithelial apoptosis. Endoscopically, the mucosa may show a brownish discoloration in a moire pattern.

On biopsy, melanosis coli shows characteristic pigment-laden macrophages within the mucosa on PAS staining. The histologic differential diagnosis of mucosal pigmentation is: lipofuscin (melanosis coli), hemosiderin-laden macrophages, and melanin (rare). A melanosis coli with pseudoobstruction syndrome has also been described.

Prognosis

No adverse effects or consequences of melanosis coli have been identified.

For some authors, melanosis coli is associated with an increased risk of colorectal tumors but is not agreed to be a pre-cancerous lesion.

References

- Pseudo-obstruction with pitch black colon—a very rare presentation of melanosis coli. Malik AH, Andrabi SI, Niayesh M. Ulster Med J. 2008 Jan;77(1):54-5. PMID: 18269120