Pancreatic Adenocarcinoma in a Patient with IgG4-Related Autoimmune Pancreatitis: Diagnostic Challenge

Introduction: IgG4-related autoimmune pancreatitis (AIP) type 1 is a fibroinflammatory condition. An atypical case of pancreatic adenocarcinoma arising in a patient with IgG4-related AIP, which progressed despite corticosteroid therapy, raising the hypothesis of a missed malignancy at initial presentation or tumor development in the setting of chronic inflammation is reported. Case report: A 46-year-old male presented with abdominal pain, fever, and jaundice. Imaging revealed a pancreatic head mass with calcifications, pancreatic tail atrophy, and peripancreatic lymphadenopathy, raising suspicion of malignancy. During hospitalization for diagnostic workup, the patient developed cholangitis. Magnetic resonance cholangiopancreatography revealed a common bile duct stricture, managed with endoscopic retrograde cholangiopancreatography and biliary stent placement. An endoscopic ultrasound-guided biopsies were non-diagnostic. An exploratory laparotomy with open biopsy confirmed IgG4-related AIP. Despite corticosteroid therapy, the patient showed clinical deterioration with worsening abdominal pain, progressive biliary strictures, and significant weight loss. During follow-up, biliary stent exchanges became increasingly difficult due to stricture progression. Another endoscopic ultrasound-guided biopsy ultimately confirmed pancreatic adenocarcinoma. The patient was referred for palliative chemotherapy. Conclusion: The diagnosis of IgG4-related pancreatitis must be carefully established, and lack of treatment response warrants diagnostic reevaluation, as in this case, where it ultimately represented pancreatic malignancy.