The most common cause of melanosis coli is the extended use of laxatives, this darkening of the colonic mucosa caused by the accumulation of lipofuscin particles within the macrophages of the lamina propria of the colonic mucosa as a result of long term exposure to anthraquinone-containing laxatives as Senna and other plant glycosides. However, other causes are identified, including an increase in colonic epithelial apoptosis.
This is the photograph of the colon, and there is an extremely dark appearance to the wall of the colon. This is seen in patients who have taken laxatives over many years and the pigment from the laxative gets deposited in the wall of the bowel giving an extremely dark appearance to it. This is a benign condition, not cancerous, and does not become cancerous, but often it is quite obvious.
- Melanosis coli is a misnomer, as the pigmentation is due to lipofuscin-laden macrophages - not melanin pigment. Pseudomelanosis coli is a more appropriate descriptor, but not in common usage.
The differential diagnosis of brown pigmentation of the colon is:
* Pseudomelanosis coli.
* Hemosiderin-laden macrophages (old haemorrhage).
* Melanin (rare).
