Abstract
The patient was a 66-year-old woman. Approximately 2 years after she was started on oral administration of vonoprazan fumarate (potassium-competitive acid blocker [P-CAB]) for treatment of intractable reflux esophagitis, she complained of diarrheal symptoms. Symptomatic treatment was administered for the diarrhea. However, because no symptom relief was obtained, colonoscopy (CS) was performed. In the segment from the sigmoid colon to the rectum, mucosal erythema and cat scratch signs were partially observed, while histological examination revealed an approximately 30-μm collagen band directly under the mucosal epithelium. Thus, collagenous colitis (CC) was diagnosed. Oral administration of P-CAB was discontinued, and the symptoms had disappeared one month later. When CS was repeated after another 3 months, no endoscopic abnormalities were observed. Based on histological examination, the collagen band had become thinner but persisted. Most superficial epithelium had exfoliated.
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