Rectal sparing in antibiotic-associated pseudomembranous colitis: a prospective study.

A prospective study of 22 patients with antibiotic-associated pseudomembranous colitis demonstrated that the most distal location of the pseudomembranes was noted from 0 to 25 cm from the anus in 17 patients, from 25 to 60 cm from the anus in 3 patients, and greater than 60 cm from the anus in only 2 patients. These data suggest that the pseudomembranes will be noted by the rigid sigmoidoscope in 77% of the patients and by the flexible sigmoidoscope in 91% of the patients. Colonoscopic examination beyond 60 cm from the anus was necessary for the diagnosis of pseudomembranous colitis in 2 (9%) patients.