The association between melanosis coli and pre-cancerous colorectal neoplasm is not proven yet. This study aim at investigate the clinical significance of melanosis coli (MC) on incidence and pathology of colorectal neoplasm.

This is a retrospectively review of patients diagnosed with melanosis coli by colonoscopy at the University of Hong Kong–Shenzhen Hospital. Patient demographics, incidence and pathology of colorectal neoplasm were compared with controlled group by case controlled matching algorithm.

From August 2012 to December 2015, a total of 98 patients diagnosed with melanosis coli by endoscopic examinations were included in our study. 252 cases diagnosed without melanosis coli at the same period of time were selected as control group by case controlled matching. Moderate or severe melanosis coli are more frequently involved whole colon than mild lesion (P=0.01). 40.8 % patients of MC group suffering from colorectal neoplasm, while it was 23.0% in control group (P=0.001). And more polyps were found over transverse colon, descending colon, and cecum in MC group than in the control group (P<0.05). Of all polyps, percentage of adenomas were 80% and 67.9% in MC group and control group respectively (P=0.117). No significant difference was demonstrated in the incidence and pathology of colorectal polyps between different disease degrees of melanosis coli, as well as between different disease distribution of melanosis coli (P>0.05).

Patients with melanosis coli having a higher incidence of colonic polyps, therefore more frequent surveillance colonoscopy can potentially decrease the incidence of colorectal cancer in this group of patients. Whereas disease severity and distribution of melanosis coli have no significant impact on incidence and pathology of colonic polyps.