E-Newsletter Issue 12: Brainteaser/image of the month
This was the mucosal appearances throughout the colon in a 49-year-old woman undergoing investigations for abdominal pain and diarrhoea.
What is the cause of the pigmentation?
- melanin
- lipofuscin
- hemosiderin
- food coloring additives
- cyanosis
Explanation
Option B is correct. This is a case of melanosis coli which was first described in 1857 by the German pathologist Dr. Rudolf Virchow1. "Virchow's sign" is well known to most clinicians (palpable supraclavicular node in gastric cancer - also known as Troisiers sign).
The pigmentation in melanosis coli is thought to be due to deposits of apoptotic cells, which are ingested by adjacent macrophages within the epithelium. These macrophages migrate in the lamina propria, where lysosomes convert the remains of the cells into lipofuscin pigment. It follows that the term "melanosis" is incorrect as the pigment is not melanin!
The condition is associated with the use of anthraquinones and bisacodyl. It spontaneously declines within a few years after discontinuation of the laxative.
Paradoxically, it is actually easier to detect adenomas in patients with melanosis coli. For some reason, the adenomas remain unpigmented as demonstrated in the picture of a small tubular adenoma below.
1 Wittoesch JH, Jackman RJ, McDonald JR. Melanosis coli: general review and a study of 887 cases. Dis Colon Rectum 1958;1:172-180
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