Anal lesions complicating Crohn disease.

Of 503 patients with Crohn disease seen at the New York Hospital-Cornell Medical Center, 138 (28%) developed an anorectal abscess, anal fissure, or anal fistula during the course of their disease. In 9.3% of patients the anal lesion preceded the onset of intestinal symptoms by two weeks to 12 years. Patients in our series with large bowel disease were twice as likely to develop an anal lesion as were patients with small bowel disease. Likewise, patients with large bowel disease were twice as likely to have had an anal lesion as a presenting symptom. A patient with an anal lesion, however, was more apt to develop small bowel disease simply because the small bowel was a far commoner site of Crohn disease in this series. The cause of the anal lesions is still not clear. Specific evidence of Crohn disease was not found in histological examination of material from any of the patients.