Pseudomembranous colitis: Not always Clostridium difficile.

Although Clostridium difficile infection is the cause of most cases of pseudomembranous colitis, clinicians should consider less common causes, especially if pseudomembranes are seen on endoscopy but testing remains negative for C difficile or if presumed C difficile infection does not respond to treatment. Histologic review of colonic mucosal biopsy specimens can provide clues to the underlying cause.