A 50-year-old woman with colonoscopy showing dark discoloration of the entire colon with pale patches in which lymph follicles shine through—most likely etiology?

• A. Ischemic colitis
• B. C difficile colitis
• C. Ulcerative colitis
• D. Laxative abuse

Answer: (D)

This endoscopic pattern is classic for melanosis coli from laxative abuse. Chronic stimulant laxatives cause increased epithelial turnover and apoptosis, and macrophages in the lamina propria ingest the apoptotic debris and pigment, leading to a dark brown to black discoloration of the colonic mucosa. The pale patches where lymphoid follicles shine through occur because these pigmented areas surround relatively nonpigmented lymphoid tissue, so the follicles pop as light islands. This appearance helps distinguish it from other causes: ischemic colitis would show segmental pale and hemorrhagic mucosa with possible коммун changes; C difficile colitis presents with pseudomembranes; ulcerative colitis shows diffuse inflammatory mucosal changes with ulcers rather than pigmentation. Therefore, laxative abuse is the most likely etiology.