Antibiotic-associated colitis with normal-appearing rectum.

A patient was recently seen with pseudomembranous colitis. He had severe disease of the proximal colon, with normal-appearing rectum and distal sigmoid, three weeks after administration of prophylactic antibiotics for surgery. The patient improved after discontinuing the antibiotics. Fiberoptic colonoscopy should be performed in patients suspected of having pseudomembranous colitis, even when sigmoidoscopy results are normal.