Melanosis coli has long been considered as a harmless pigmentation of the colorectum associated with the use of laxatives containing anthraquinone. Recent experimental and clinical studies, however, have provided some evidence of a possible association between melanosis coli/laxative use and colorectal cancer.
Methods: In 2.229 consecutive patients we retrospectively analyzed the association of melanosis coli and laxative use with colorectal neoplasia. All the patients had undergone total colonoscopy, and the colorectal neoplasias had been examined histopathologically in accordance with the WHO classification. Information concerning laxative use, bowel habits and family history of colorectal cancer was obtained from the medical records. The statistical analysis was done using the Mantel-Haenszel-test for linear association.
Results: The presence of colorectal cancer was not associated with melanosis coli or laxative use. However, colorectal adenomas were found significantly more frequently in patients with melanosis coli than in those without melanosis (p = 0.0002). But adenomas associated with melanosis coli were significantly smaller than those not associated with melanosis (p < 0.0001), and were located predominantly in the proximal colon (p = 0.0002). In the patients with melanosis coli the relative risk was significantly higher for tubular (1.80; 95% CI: 1.26-2.56) and tubulovillous adenomas (2.03; 95% CI: 1.09-3.76), but not for villous adenomas. No significant differences were found in the grade of dysplasia of adenomas in patients with, and those without, melanosis coli.
Conclusion: There appears to be no association between colorectal cancer and melanosis coli or laxative use. Colorectal adenomas are more frequently found in patients with melanosis coli. Colorectal adenomas do not contain the melanin-like pigmentation. The association of adenomas with melanosis coli can be explained by the ease of detection of even tiny polyps as white spots within a dark-colored colonic mucosa.