This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
[{'content': "Toxic megacolon is seen in – \nSelect and explain. \nA. Chronic nonspecific ulcerative colititis, B. Crohn's disease, C. Colonic diverticulosis, D. Hamartomatous polyp", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Features of UC \n\nUlcerative colitis involves the rectum and extends proximally.\nIn severe cases, entire colon may be involved Pancolitis.\nIt is a disease of continuity, and skip lesions are not found.\nIn some patients, distal ileum may also develop mucosal inflammation → backwash ileitis.\nOnly mucosa and submucosal layers of the colon are involvement, deep layer are not involved usually.\nIsolated islands of regenerating mucosa bulge upward to create pseudopolyp.\nThere are a superficial mucosal ulcer but they are not serpentine as seen in CD.\nNeutrophilic infiltration into crypts leads to the formation of crypt abscess.\nIn sever cases of UC, toxic damage to the muscular propria and neural plexus lead to complete shutdown of neuromuscular function → \xa0colon progressively swells to create toxic megacolon.\nThere may be epithelial dysplasia with progression to frank carcinoma.', 'role': 'assistant'}]