Melanosis Coli: Relation to Apoptosis in Pathogenesis

Sung, Sun Hee; Koo, Hea Soo; Han, Woon Sup

Abstract

Melanosis coli is characterized by a dark brownish discoloration of the colonic mucosa. Its pathogenesis is still unknown. Recently it was proposed that the apoptosis of mucosal epithelium due to habitual use of laxatives play an important role for induction of melanosis coli. We studied clinicopathologic aspects of 12 cases of melanosis coli and analysed the histochemical and immunohistochemical characteristics of them. Results are as follows. : Mean patient's age was 53.5, and the male:female ratio was 4:8. Nine patients had a history of constipation, and all of these had administrated various kinds of laxatives. The severity of discoloration was correlated with the duration of constipation and age. There was no difference of anatomical distribution in colon. Other remarkable mucosal lesions were not accompanied. On pathologic examination, all cases showed frequent yellow-brown pigment laden cells in lamina propria. These pigments were positive for periodic acid Schiff stains, Fontana Masson stains, and Victoria blue stains, however they were negative for prussian blue stain. On immunohistochemical stainings pigmented cells were positive for CD68, and negative for S-100 protein and neuron specific enolase. These results indicate that they are macrophages. On ultrastructural examination pigmented cytoplasms were filled with variable sized electron dense granules including irregulary round deformed membranous structures, lipid vacuoles. Apoptosis of mucosal epithelium was noted in 5 cases. These findings suggest that apoptosis is the significant pathologic process in the progression of some cases of melanosis coli.