Background and Aims: Eosinophils are implicated in the pathogenesis of inflammatory bowel disease (IBD). A subset of IBD patients develops blood eosinophilia, and the clinical profile of these patients is undefined. We sought to characterize IBD patients with and without eosinophilia. Methods: We studied a prospective registry of 1,176 IBD patients followed in a tertiary referral center. Patients who developed eosinophilia at any time were identified by electronic medical record query. We performed a chart review case-control study comparing patients with recurrent eosinophilia versus randomly selected disease-matched patients with no history of eosinophilia. Histological analysis was performed on selected cases and controls. Results: Eosinophilia at any time was more prevalent in ulcerative colitis (UC) patients than Crohn's disease patients (22.2 versus 12.7 %), as was recurrent eosinophilia (3.4 versus 0.7 %). UC patients with recurrent eosinophilia were predominantly male compared with the control UC population (81.3 versus 46.9 %) and had higher rates of colectomy for either medically refractory disease or dysplasia/cancer than control UC patients (56.3 versus 15.6 %). Primary sclerosing cholangitis (PSC) occurred in 37.5 % of UC patients with recurrent eosinophilia compared with only 3.1 % in the UC controls. Histological analysis of random diagnostic samples from UC patients with recurrent eosinophilia demonstrated a normal eosinophil pattern as seen in the control UC population. Conclusions: Eosinophilia-associated UC is a subgroup of IBD associated with severe colitis and PSC. Further studies are warranted to characterize molecular mechanisms underlying eosinophilia- associated UC and to determine optimal approaches for therapy.
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