Can the wet suction technique change the efficacy of EUS-FNA for diagnosing autoimmune pancreatitis type 1? A prospective single-arm study

Abstract Background: Other than surgical biopsy, endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) is the only method for histologically diagnosing autoimmune pancreatitis (AIP). However, adequate specimens are difficult to obtain. Recently, more adequate specimens were reported to be obtained with a wet suction technique (WEST) of EUS-FNA than with the conventional method of EUS-FNA. This study aimed to histologically diagnose AIP by EUS-FNA with a WEST. Methods: Eleven patients with possible type 1 AIP between February 2016 and August 2018 underwent WEST EUS-FNA (WEST group) with four punctures with 19 or 22 G needles. As a historical control, 23 type 1 AIP patients who underwent no fewer than four punctures with 19 or 22 G needles were selected (DRY group). Patient characteristics and histological findings were compared between the two groups. Results: Three histopathological items of the International Consensus Diagnostic Criteria were significantly greater in the WEST group than the DRY group (n (%), lymphoplasmacytic infiltrate without granulocytic infiltration: 9 (81.8) vs 6 (26.1), p value=0.003, storiform fibrosis: 5 (45.5.) vs 1 (4.3), p value=0.008, abundant (>10 cells/HPF) IgG4-positive cells: 7 (63.6) vs 5 (21.7), p value=0.026). Level 1 or level 2 histopathological findings were observed more in the WEST group than in the DRY group (n (%) 8 (72.7) vs 3 (13.0), p value=0.001). Conclusions: WEST EUS-FNA was more useful than standard EUS-FNA for histologically diagnosing AIP.Trial registration: UMIN000019768Date of registration: November 12, 2015