S187 Endoscopic Ultrasound and Clinicodemographic Features to Distinguish Pancreatic Ductal Adenocarcinoma From Autoimmune Pancreatitis

Introduction: Autoimmune pancreatitis (AIP) often mimics pancreatic ductal adenocarcinoma (PDAC), posing a diagnostic challenge. AIP, a rare but distinct pancreatitis, typically responds to corticosteroids. It is suspected in patients with obstructive jaundice, a pancreatic mass, or diffuse inflammation—features overlapping with PDAC. Accurately distinguishing these conditions is essential to avoid unnecessary surgery in AIP and ensure timely intervention in PDAC. This study aims to identify clinicodemographic and endoscopic ultrasound (EUS) features to distinguish AIP from PDAC. Methods: We performed a retrospective database review of all cases with PDAC and AIP diagnosed and managed at a single institution. PDAC cases were confirmed via histopathology obtained during EUS-guided fine-needle biopsy. AIP diagnoses were confirmed based on histopathology, response to steroids, IgG4 staining of pancreatic tissue or extrapancreatic involvement. Results: The study included 24 AIP and 272 PDAC patients. Both predominantly affected men: AIP (67%) vs PDAC (56%) (P = 0.32). Mean BMI was similar (AIP: 26.0 vs PDAC: 24.4; P = 0.08), but BMI <25 was more common in PDAC (9.6%) than AIP (4.2%) (P = 0.04). AIP patients were younger (mean 61 vs 70 years; P < 0.0001). Diabetes prevalence was similar (AIP: 46% vs PDAC: 42%). Only 1 AIP patient had IBD. Diffuse pancreatic enlargement was more frequent in AIP (44% vs 3.6%, P < 0.0001); ductal dilation was more common in PDAC (60% vs 11%, P = 0.009). PDAC cases showed focal masses (94%), while AIP showed diffuse, hypoechoic changes. Liver metastases occurred in 16.9% of PDAC patients. IgG4 >140 mg/dL was seen in 54% of AIP cases; recurrence occurred in 25%. Age > 73 and focal lesions were strongly associated with PDAC. Lesions >30 mm had a 96% likelihood of PDAC; even lesions <30 mm had a 98% chance. The pancreatic head was the most commonly affected site in both conditions. Conclusion: Clinicodemographic and EUS features can help differentiate AIP from PDAC. Older age, focal lesions, and pancreatic duct dilation were more associated with PDAC, while diffuse pancreatic changes, lymphadenopathy, and elevated IgG4 levels favored AIP. Although lesion size >30 mm was associated with PDAC, the probability remained high even for smaller lesions, limiting its utility as a distinguishing factor. A multidisciplinary approach remains essential to improve diagnostic accuracy and guide management avoiding unnecessary surgeries in AIP while ensuring timely treatment in PDAC.