A woman, aged 83, was investigated by colonoscopy because of a family history of colorectal cancer. Abdominal symptoms were relatively minor but included intermittent abdominal cramps and abdominal ‘bloating’. At colonoscopy, she had multiple small nodules, 1–2 mm in diameter, in the ascending colon and cecum as shown in Fig. 1. The remainder of the colon was normal. Histological evaluation of biopsies from the ascending colon revealed a dense infiltrate of eosinophils and other inflammatory cells in the lamina propria (Fig. 2). The eosinophil count was >100 per high power field. The diagnosis was that of eosinophilic colitis. She had a normal hemoglobin and white cell count and a normal eosinophil count in peripheral blood. No specific treatment was given as it was uncertain whether eosinophilic colitis was responsible for her symptoms.

Eosinophils can accumulate in the large bowel in a variety of disorders including eosinophilic colitis, eosinophilic (allergic) colitis of infancy, vasculitis, drug reactions, helminth infections and inflammatory bowel disease. Eosinophilic colitis is a rare disorder, at least in adults, and its relationship to eosinophilic esophagitis, eosinophilic gastroenteritis and food allergy continues to be unclear. The symptoms of eosinophilic colitis are highly variable but can include diarrhea, abdominal cramps, anorexia and weight loss. At colonoscopy, some patients have lymphonodular hyperplasia while others have endoscopic features of mild colitis including mucosal edema, patchy erythema and loss of vascularity. Changes can occur throughout the colon but tend to be more prominent in the proximal colon and rectum. The histological features include focal aggregates of eosinophils in the lamina propria, crypt epithelium and muscularis mucosa. The majority of patients (60%–80%) have an increase in the eosinophil count in peripheral blood. In relation to management, infants with eosinophilic (allergic) colitis usually improve rapidly after withdrawal of the offending dietary trigger. In contrast, the response of adults to dietary modification is less clear and those with more severe symptoms are often treated with corticosteroid drugs. Experimental drugs for the treatment of eosinophilic syndromes include newer antihistamines, leukotriene receptor antagonists, and monoclonal antibodies against interleukin-5 and IgG1.

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