Refractory or fulminant CDAD develops in some patients, leading to systemic inflammatory response (characterized by leukocytosis, hypotension, anasarca, and renal failure). The most devastating complication of CDAD is toxic megacolon. In this condition the large bowel becomes massively dilated (> 7 cm) with characteristic thumbprinting due to submucosal edema. These patients are at high risk of perforation and need surgical consultation to be assessed for emergent colectomy. Mortality is high, approximately 50%. Unfortunately, atypical presentations of toxic megacolon are not unusual. In one study of patients requiring colectomy, 20% had a negative C difficile antigen test, and almost 40% had no diarrhea. Therefore, CDAD should be entertained in any patient with colonic dilation.