This patient most likely has Crohn disease. In about 10% of patients, especially those who are young, the onset of the disease is abrupt and may be mistaken for acute appendicitis. Appendectomy is indicated in such patients as long as the cecum at the base of the appendix is not involved. Interestingly, about 90% of patients who present with the acute appendicitis-like form of regional enteritis will not progress to development of the full-blown chronic disease. Thus, resection or bypass of the involved areas is not indicated at this time. Patients with regional enteritis usually have a chronic and slowly progressive course with intermittent symptom-free periods. The usual symptoms are anorexia, abdominal pain, diarrhea, fever, and weight loss. Extraintestinal syndromes that may be seen include ankylosing spondylitis, polyarthritis, erythema nodosum, pyoderma gangrenosum, gallstones, hepatic fatty infiltration, and fibrosis of the biliary tract, pancreas, and retroperitoneum.