Correct answer: b.
Discussion
Naturally, this is a case of melanosis coli, which was first described in 1857 by the German pathologist Dr Rudolf Virchow.1 Dr Virchow’s name will be familiar to most clinicians and perhaps he is best known for describing Virchow’s node, an enlarged supraclavicular node, classically found in a patient with gastric cancer (also known as Troisier’s sign), although the node may be due to a multitude of pathologies.
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 into 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!
Melanosis coli is associated with the use of anthraquinones and bisacodyl. The condition spontaneously resolves within a few years of stopping the laxative.
Paradoxically, it is actually easier to detect adenomas in patients who have melanosis coli. For some reason, adenomas remain unpigmented in these patients, as demonstrated in the photograph of a small tubular adenoma.
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