Aphthous lesions in Crohn's disease, endoscope view. These lesions (red and white discoloured areas at upper centre and centre left) are in the small intestine. Crohn's disease causes inflammation, thickening, and ulceration of the intestinal tract. Its cause is unknown and there is no cure. Symptoms include abdominal pain, diarrhoea and the malabsorption of food, leading to weight loss. An aphthous ulcer (a small painful sore) is the earliest and most characteristic endoscopic finding in Crohn's disease.