Clinicopathological study of surgically treated non-neoplastic diseases of the pancreas with special reference to autoimmune pancreatitis

Purpose: After the popularization of serum immunoglobulin G4 (IgG4) measurement and endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) in our institute, surgical resection for non-neoplastic diseases of the pancreas became less common. Although the incidence of such false-positive cases was clarified in the 10-year period after introduction of these measures (2009–2018), these data were not compared with the 30 years before 2009 (1979–2008). This study was performed to determine the percentage of autoimmune pancreatitis (AIP) that was included during the latter period and how the numbers of false-positive cases differed between the two periods. Methods From 1979 to 2008, 51 patients had clinical suspicion of pancreatic carcinoma (false-positive disease). Among these 51 patients, 32 non-alcoholic patients who had tumor-forming chronic pancreatitis (TFCP) were clinically, histologically, and immunohistochemically compared with 11 patients who had TFCP during the latter 10-year period. Results Retrospective IgG4 immunostaining of TFCP revealed 14 (43.8%) cases of AIP in the former 30 years versus 5 (45.5%) in the latter 10 years. There were 32 (6.7%) cases of TFCP among 675 patients in the former 30 years and 11 (0.9%) among 1289 patients in the latter 10 years. Conclusions When the TFCP ratio of pancreatic resections and the AIP ratio of TFCPs were compared between the two periods, the TFCP ratio was 4.7% versus 0.9% and the AIP ratio was 43.8% versus 45.5%, respectively. These findings indicate that IgG4 measurement and EUS-FNA are imperative for the diagnosis of TFCP.