Atypical melanosis coli resembling the appearance of cheetah skin

A 61-year-old woman was referred for colonoscopy because she had been suffering from diarrhea with fatigue and weight loss over a 2-month period. The patient had a 20-year history of chronic constipation, which she treated intermittently with herbal products (Rhamnus purshianus and Aloe ferox). She stopped taking the herbal products at the onset of diarrhea.

On colonoscopy, the color of the colon mucosa was normal except for the proximal right colon and the cecum. At this level, imaging revealed multiple, dark brown, oval, rounded macular lesions of variable size (1 – 8 mm) and diffuse distribution, surrounded by normal-appearing mucosa ([Fig. 1], [Fig. 2], and [Fig. 3]). Biopsy specimens of the lesions showed an accumulation of brown pigment within macrophages in the lamina propria, which was consistent with a diagnosis of melanosis coli ([Fig. 4] and [Fig. 5]).

Fig. 1 Findings in the right part of the colon on conventional colonoscopy. Multiple dark brown macules with an oval, rounded shape are surrounded by normal-appearing mucosa, resembling a cheetah’s skin.

Fig. 2 Close-up view of lesions with conventional colonoscopy. The patches vary in size, with some being very small and barely noticeable.

Fig. 3 Close-up view of lesions with conventional colonoscopy. Some are extremely well defined and of a darker color, whereas others have a lighter color and more diffuse edges.

Fig. 4 Histological findings of the colon biopsy (hematoxylin and eosin, × 40). Localized group of histiocytes in the lamina propria with brown pigment in their cytoplasm, which is consistent with melanosis coli.

Fig. 5 Histological findings of the colon biopsy (hematoxylin and eosin, × 100). Pigment-laden histiocytes are arranged back to back in the lamina propria, surrounding nerve fascicles.

Melanosis coli is a benign condition occurring in the colon as a result of the intake of products that contain anthraquinone. This substance is a component of laxative products such as cascara sagrada, senna, aloe, or rhubarb. Extensive consumption leads to the accumulation of macrophages laden with brown lipofuscin pigment in the lamina propria. This produces a typically diffuse, dark brown discoloration of the mucosa, predominantly in the cecum and the right part of the colon. Its appearance has often been likened to a crocodile or snake skin or a starry sky in the rectosigmoid. Pigmentation may disappear a year after suspension of anthraquinones [1] [2] [3].

Unusually, in this case the distribution of diffuse pigmentation was not uniform but patchy, and there were oval, rounded, and pointed deposits surrounded by mucosa of a normal color, resembling the skin of a cheetah, an appearance that has not been described previously. This atypical appearance may be caused by the temporary suspension of anthraquinone.

Endoscopy_UCTN_Code_CCL_1AD_2AJ

Competing interests: None

• References

• 1 Kew ST, Chakravarthi S. Images in clinical medicine: melanosis coli. N Engl J Med 2013; 368: 2303
• 2 Freeman HJ. “Melanosis” in the small and large intestine. World J Gastroenterol 2008; 14: 4296-4299
• 3 Benavides SH, Morgante PE, Monserrat AJ et al. The pigment of melanosis coli: a lectin histochemical study. Gastrointest Endosc 1997; 46: 131-138