Nationwide epidemiological survey of autoimmune pancreatitis in Japan in 2021

To update the clinic-epidemiological features of autoimmune pancreatitis (AIP) in Japan, we conducted the fifth nationwide survey.

We performed a two-stage survey of patients with AIP who were treated at selected hospitals in 2021. The first-stage survey estimated the total number of patients with AIP, and the second-stage survey analyzed detailed clinical characteristics.

The estimated number of patients with AIP in 2021 was 16,750 (prevalence, 13.3 per 100,000 persons), representing a 25% increase from 2016. The number of newly diagnosed cases was 4210 (annual incidence, 3.4 per 100,000 persons). Clinical data were available for 2833 patients. The male-to-female ratio was 3.32:1, and the mean age in 2021 and the mean age at AIP diagnosis were 71.2 and 66.3 years, respectively. At diagnosis, 58.6% of patients were symptomatic, approximately half of whom presented with jaundice. Other organ involvement was observed in 67.8% of patients, most commonly sclerosing cholangitis. Histopathological examination was performed in 84.1% of cases, predominantly using endoscopic ultrasonography-guided tissue acquisition. Initial glucocorticoid therapy was administered to 84.2% of patients, and 93.8% received maintenance therapy. Kaplan-Meier analysis demonstrated a cumulative relapse incidence of 12.5%, 20.7%, 36.0%, 44.0%, 53.3%, and 68.9% at 3, 5, 10, 15, 20, and 25 years, respectively. Long-term overall survival was favorable; however, malignancies accounted for 40% of deaths.

This nationwide survey updates the epidemiological and clinical characteristics of AIP in Japan. Patient numbers continue to rise, and the high cumulative risk of relapse underscores the need for second-line therapies beyond glucocorticoids.