Nationwide Epidemiological Survey of Autoimmune Pancreatitis in Japan

Objectives: To clarify the clinicoepidemiological features of autoimmune pancreatitis (AIP) in Japan, the nationwide survey was conducted. Methods: Patients with AIP who had visited the selected hospitals in 2007 were surveyed. Autoimmune pancreatitis was diagnosed according to the Japanese clinical diagnostic criteria 2006. The study consisted of 2-stage surveys: the number of patients with AIP was estimated by the first questionnaire and their clinical features were assessed by the second questionnaire. Results: The estimated total number of AIP patients in 2007 was 2790 (95% confidence interval, 2540-3040), with an overall prevalence rate of 2.2 per 100,000 populations. The number of patients, who were newly diagnosed as AIP, was estimated to be 1120 (95% confidence interval, 1000-1240), with an annual incidence rate of 0.9 per 100,000 populations. Sex ratio (male to female) was 3.7, and the mean (SD) age was 63.0 (11.4) years. Among the 546 patients whose clinical information was obtained, 87.6% of the patients presented high serum immunoglobulin G4 levels (>= 135 mg/dL), and 83% received steroid therapy. Conclusions: The data represent the current clinical features of AIP in Japan. From the results, most AIP patients in Japan can be categorized to type 1 AIP according to the recent classification of AIP.