Nationwide epidemiological survey of autoimmune pancreatitis in Japan in 2021.

BACKGROUND

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

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.