Crohn's disease. Axial coloured magnetic resonance imaging (MRI) scan of the intestines of a patient suffering from Crohn's disease. The inflamed colon can be seen at upper left (orange). Crohn's disease causes inflammation, thickening and ulceration of the digestive tract, most often the small intestine and the colon (large intestine). Its cause is unknown, but may be linked to an overactive immune system. Symptoms include abdominal pain, diarrhoea and the malabsorption of food, leading to weight loss. Crohn's disease cannot be cured but can be controlled with anti-inflammatory drugs, nutritional supplements and occasionally surgery.