Differentiation Between Autoimmune Pancreatitis and Pancreatic Carcinoma By Endoscopic Retrograde Cholangiopancreatography (ERCP)

Abstract

Background and Aim: Autoimmune pancreatitis (AIP) is usually manifested on abdominal US and CT scans as diffuse enlargement of the pancreas, and as diffuse irregular narrowing of the main pancreatic duct (MPD) by ERCP, however, there have been recent reports of difficulty in diagnosing AIP because of atypical imaging findings and that it is sometimes difficult to differentiate AIP from pancreatic carcinoma (PCa). In the present study we reviewed the ERCP images of AIP patients and PCa patients in an attempt to identify findings that would make it easier to differentiate AIP from PCa. Methods: The subjects were 38 consecutive patients diagnosed with AIP on the basis of the revised diagnostic criteria for AIP proposed in 2006 (37/38) or the histological findings (1/38), and 38 patients diagnosed with PCa, 32 based on the histological findings in the surgical specimen and 6 by various imaging methods, and we compared the ERCP findings in the pancreatic duct and bile duct in the two groups. Results: 1. ERCP revealed narrowing of the MPD in 37 (97%) of the 38 AIP patients and an obstructed MPD in the other patient (3%), as opposed to a stenosed MPD in 24 (63%) of 38 the PCa patients and an obstructed MPD in the other 12 (32%) patients (p = 0.002 and p = 0.001, respectively). 2. ERCP showed a significantly greater length of narrowed or stenotic MPD in AIP than in PCa (p < 0.001). 3. The prevalence of the presence of side branches was significantly higher in AIP than in PCa (p < 0.001). 4. An upstream MPD with a maximal diameter < 4 mm was found in 33 (89%) of the 37 AIP patients with a narrowed MPD, but in only 5 (21%) of the 24 the PCa patients with a stenotic MPD (p < 0.001). 5. The bile duct findings showed a significantly higher prevalence of common bile duct (CBD) stricture with right side deviation (so-called double duct sign) in the PCa patients than in the AIP patients (p = 0.004). 6. Discriminant analysis based on these findings correctly identified 36 of the 38 AIP patients and 33 of the 38 PCa patients. 7. It was impossible to make differentiation from AIP in several PCa patients in whom ERCP showed both an MPD that was stenotic for more than 5 cm of its length and the presence of side branches. Conclusions: It seems possible to make the differential diagnosis between AIP and PCa in many cases based on the ERCP findings in regard to the presence of side branches, length of the MPD that was narrowed or stenotic, the caliber of the upstream MPD, and the character of the bile duct stricture. However, some PCa patients have ERCP findings similar to those of AIP patients.