Melanosis Coli due to Rhubarb Supplementation

CASE REPORT

A 67-year-old woman with a history of left-sided ulcerative colitis, sclerosing cholangitis, sclerosing pancreatitis, slow transit constipation, recurrent stenosis of the pancreatic orifice, and Waldenstrom's macroglobulinemia presented for her yearly colonoscopy for colorectal cancer screening. Her outpatient medications at the time of colonoscopy included acetaminophen, alprazolam, calcium/vitamin D supplement, dexlansoprazole, estradiol, as needed ondansetron, pancrelipase before meals, and as need tramadol. Her colonoscopy showed dark black pigmentation, and it was virtually impossible to see anything with standard illumination on the colonoscope, and no active ulcerations were noted (Figure 1). She was asymptomatic with stable vitals. She reported using natural fiber supplement that has rhubarb in it. She denied any laxative use. She stopped using rhubarb extract and underwent repeat colonoscopy 1½ years later, which showed profound improvement in the previously noted dark black pigmentation (Figure 2). None of the existing outpatient medications were changed or stopped between the colonoscopies.

Figure 1.

Initial colonoscopy showing dark black pigmentation without any active ulcerations.

Figure 2.

Repeat colonoscopy with profound improvement in the dark black pigmentation noted on initial colonoscopy.

It was thought that the anthranoid compound contained within the rhubarb was the likely source of her melanosis coli. A thorough search of the literature was done, and none of her outpatient medications were found to be associated with melanosis coli. No clear association was found between inflammatory bowel disease and melanosis coli. Only one small retrospective study was found which indicated a possible association between inflammatory bowel disease and melanosis coli; however, there are no confirmatory retrospective studies, prospective studies, or further case reports documenting this finding. In our patient, the ulcerative colitis was reasonably well controlled with left-sided chronic colitis and focal active colitis on the biopsies. This does not correlate with the extensive melanosis coli noted on the endoscopy.

Melanosis coli is a distinct endoscopic finding which is often associated with chronic laxative use in which dark cellular pigment deposits in the lamina propria of the colon.^1,2 This patient reported taking rhubarb for years. The active ingredient in rhubarb is anthraquinone which causes injury to the colonic epithelial cells, resulting in melanosis coli.^1,2 The anthranoid products pass unabsorbed throughout the bowel until they reach the large intestine, where they are converted to their active forms.¹ The anthranoid products damage the epithelial cells, causing changes in absorption, secretion, and motility.³ The active forms of anthranoid products further cause injury to the epithelial cells, leading to apoptosis (a form of cell death), which releases darkly cellular pigment (lipofuscin) that are taken up by macrophages.^1–3 The pigment deposition results in a distinctive dark brown to black staining of the lining of the large intestine. The condition is benign and reversible on discontinuing the implicating agent.^2,3 Disappearance of the pigment usually occurs within a year after stopping anthraquinone use.^1–3

DISCLOSURES

Author contributions: JS Klair performed the literature review, drafted the case, critically revised the manuscript, and is the article guarantor. S. Chandra performed the literature review, drafted the case, and critically revised the manuscript. FC Johlin critically revised the manuscript.

Financial disclosure: None.

Informed consent was obtained for this case report.