In the International Consensus Diagnostic Criteria (ICDC), autoimmune pancreatitis (AIP) is classified into types 1 and 2, and its definite histopathology diagnosis can be made based only on surgical or core biopsy specimens. Although EUS-guided FNA (EUS-FNA) biopsy is a safe technique for the collection of pancreatic tissue, no consensus viewpoint has been reached with regard to the role of EUS-FNA biopsy in the diagnosis of AIP. This study investigated the utility of pancreatic tissue collected by EUS-FNA biopsy by using a standard 22-gauge aspiration needle in the diagnosis of AIP.

Patients with suspected AIP were prospectively enrolled in Nagoya University Hospital and Nagoya University–affiliated institutions. Pancreatic tissue was collected from each by EUS-FNA biopsy with a standard 22-gauge aspiration needle.

Fifty patients were registered, including 45 with a final diagnosis of AIP. Lymphoplasmacytic infiltration and abundant immunoglobulin G₄–positive plasmacyte infiltration (>10/high-power field) were detected in 36 (72%) and 27 (54%) patients, respectively. Obliterative phlebitis and storiform fibrosis were not detected in our study. Granulocytic epithelial lesions (GEL) were observed in 3 patients. The sensitivity, specificity, positive predictive value, and negative predictive value of EUS-FNA biopsy to definitively diagnose AIP were 7.9% (3/38), 100% (12/12), 100% (3/3), and 25.5% (12/47), respectively. Pathology evaluation of pancreatic tissue collected by EUS-FNA biopsy improved the diagnostic accuracy in 8 (16%) of the 50 patients.

In this study, EUS-FNA biopsy by using a standard 22-gauge aspiration needle is not an effective diagnostic method for most patients with AIP. The combination of level 2 histology diagnosis of AIP with other findings specified in the ICDC slightly improved the diagnostic accuracy, although it still remains insufficiently accurate for routine clinical use.(Clinical trial registration number: 000006297.)