This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Surgery
The indications of colonoscopy in a patient with ulcerative colitis are all of the following except 
Select and explain. 
A. Diagnosis of the extent of inflammation, B. Differentiating it from Crohn's disease, C. Diagnosis of toxic megacolon, D. Monitoring the responds to treatment
C: Diagnosis of toxic megacolon
Answer: C: Diagnosis of toxic megacolon 
Explanation: .Colonoscopy is of value to rule out carcinoma. It is easiest and most direct method in establishing the diagnosis. Colonoscopy shows mucosal nodules or ulcers; caecal and ileal strictures; deformed ileo caecal valve; mucosal oedema and pseudopolyps and occasionally diffuse colitis. Biopsy can be taken to confirm the diagnosis Contraindication-Acute ulcerative colitis. ref:SRB&;S manual of surgery,ed 3,pg no 514