Nationwide epidemiological survey of autoimmune pancreatitis in Japan in 2011

Objectives To clarify the clinicoepidemiological features of autoimmune pancreatitis (AIP) in Japan, a nationwide epidemiological survey was conducted. Methods Patients with AIP who had visited selected hospitals in 2011 were surveyed. Autoimmune pancreatitis was diagnosed according to the revised clinical diagnostic criteria for AIP (Japan Pancreas Society 2011). 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 2011 was 5745 (95% confidence interval, 5325-6164), with an overall prevalence rate of 4.6 per 100,000 population. The number of patients who were newly diagnosed as AIP was estimated to be 1808 (95% confidence interval, 1597-2018), with an annual incidence rate of 1.4 per 100,000 population. The sex ratio (male to female) was 3.2, and the mean age was 66.3 (11.5). Among the 936 patients whose detailed clinical information was obtained, 86.4% of the patients presented high serum immunoglobulin G4 levels (≥135 mg/dL), and 82.3% received steroid therapy. Conclusions The data represent the current clinical features of AIP in Japan.