Therapeutic strategy for autoimmune pancreatitis.

Autoimmune pancreatitis (AIP) is a particular type of pancreatitis that is thought to have an autoimmune etiology. Before therapy for AIP is begun, accurate diagnosis of AIP is necessary. It is important to distinguish AIP from pancreatic cancer. Since there is currently no diagnostic serological marker for AIP, AIP should be diagnosed on the basis of a combination of abnormalities unique to AIP. The Japanese "Diagnostic Criteria for Autoimmune Pancreatitis 2006" require the characteristic imaging findings of AIP and that at least one of the laboratory criteria or histopathological criteria have to be present. Unlike in patients with usual chronic pancreatitis, corticosteroid therapy is frequently effective in resolving the morphological findings and the symptoms of AIP patients. Therefore, administration of oral steroid therapy has become standard therapy for AIP. Indications for steroid therapy for AIP are thought to include obstructive jaundice due to stenosis of the bile duct, associated extrapancreatic sclerosing lesions, and diabetes mellitus coincidental with AIP. Oral prednisolone is usually started at 30 mg/day and tapered by 5 mg every 1-2 weeks. Serological and imaging tests are followed periodically after commencement of steroid therapy. Patients in whom complete radiological improvement is documented can stop their medication. To prevent relapses, continued maintenance therapy with prednisolone 2.5-5 mg/day is sometimes required. Patients who relapse should be re-treated with high-dose steroid therapy. A poor response to steroid therapy should raise the possibility of pancreatic cancer and the need for further examination, including laparotomy.