Antibiotic associated pseudomembranous colitis with negative proctosigmoidoscopy examination.

Most investigators have stressed that the diagnosis of antibiotic associated pseudomembranous colitis is made by proctosigmoidoscopic examination. In our investigation, 6 patients with tissue culture evidence of a clostridial toxin in stools and either normal or only edematous rectal mucosa were studied with total colonoscopy. Five of six patients demonstrated pseudomembranes located in various areas of the colon at a time when the rectosigmoid area was uninvolved. This demonstrates the occurrence of antibiotic associated pseudomembranous colitis which can be missed by routine proctosigmoidoscopy. The incidence of rectal sparing in this disease remains undetermined. Further investigation to determine the occurrence of antibiotic colitis, response to different treatments, or sensitivity of tissue culture assays as a diagnostic aid in antibiotic associated pseudomembranous colitis must take this subgroup into account.