1591 Melanosis Coli Aids Endoscopic Differentiation of Polyp Histology in Cowden Syndrome

Abstract

INTRODUCTION: Cowden syndrome is a rare disorder related to germline mutations in the PTEN gene. Although considered a hamartomatous polyposis syndrome, emerging evidence has shown colorectal polyposis with mixed histologic types (including adenomas) to be most common. This can make endoscopic surveillance difficult. Melanosis coli is characterized by dark pigmentation of the colon. Adenomatous and hyperplastic polyps remain pale in this setting and are easily visualized, but there are no published reports on the appearance of hamartomatous polyps. CASE DESCRIPTION/METHODS: A 55-year-old man with intellectual disability was referred to our institution for consideration of colectomy due to colorectal polyposis. He was then referred to GI Genetics clinic for further evaluation prior to surgery. His history included innumerable colon polyps on previous colonoscopies. Available pathology included multiple colon polyp types including tubulovillous and tubular adenoma, serrated adenoma, hyperplastic and inflammatory polyps. His family history included twin brother with brain tumor, mother with breast cancer and stomach cancer and father with brain cancer. Examination showed macrocephaly with head circumference of 62 cm. Cowden syndrome was suspected and genetic testing was performed. This showed a pathogenic mutation in the PTEN gene and confirmed the diagnosis. Surveillance colonoscopy was performed. This showed diffuse melanosis and polyposis of the colon. There were 4 colon polyps that were pale and visually consistent with adenomas. These were resected and returned as 3 tubular adenomas and a serrated adenoma with minimally apparent melanosis on histologic assessment. There were multiple diminutive polyps throughout the colon that were dark and appeared visually consistent with hamartomas. Many of these were sampled and were consistent with hamartomatous polyps with prominent melanosis histologically. Given the ability to endoscopically differentiate between neoplastic and benign polyp histologies, ongoing surveillance colonoscopy was recommended and colectomy was avoided. DISCUSSION: Polyposis with mixed polyp histology is common in Cowden syndrome and complicates endoscopic surveillance. In our patient with melanosis coli, hamartomatous polyps remained dark and matched the surrounding mucosa while adenomas and serrated adenomas were pale and easily distinguishable. This is the first report of the appearance of hamartomas in the setting of melanosis to our knowledge.