Unusual colitides.

Colitis is an important cause of abdominal pain and diarrhoea and is the main cause of blood and mucus in the stool. The inflammation can be due to infectious or to non-infectious causes, most commonly ulcerative colitis and Crohn's disease. However, a wide variety of rarer causes of colitis also present in childhood. These include colitis or enterocolitis secondary to Hirschsprung's disease and metabolic disorders (which include Hermansky-Pudlak syndrome, glycogen storage disease type 1b and pellagra). Primary inflammation of the colon is seen in microscopic and collagenous colitis, ulcerating enterocolitis of infancy, allergic colitis and autoimmune enteropathy. The histological pattern of each of these diseases has a characteristic picture and separates them from each other from ulcerative colitis and Crohn's disease. The pathophysiology of these rare forms of colitis in childhood is not clear; but in the future they may give us an insight into the pathogenesis of large bowel inflammation, particularly when the colitis occurs secondary to an established disease.