Acute sinusoidal obstruction syndrome after 6-thioguanine therapy for Crohn's disease

6-Thioguanine (6-TG), the active metabolite of 6-mercaptopurine and its prodrug azathioprine, are thought to be responsible for clinical efficacy in the treatment of active Crohn's disease. Its use as a therapeutic agent for inflammatory bowel disease (IBD) has been limited to patients who are resistant to or intolerant of other antimetabolites. Short-term experience with this agent has not demonstrated an increased incidence of hematologic or hepatic toxicity; however long-term safety data are scarce. We herein report a patient who developed acute sinusoidal obstruction syndrome after 14 months of successful thioguanine treatment. This is the first report of such a complication in an adult treated with 6-TG for active Crohn's disease.