Multifocal Autoimmune Pancreatitis Mimicking Pancreatic Neoplasm in a Young Adult: A Diagnostic Challenge.

Autoimmune pancreatitis (AIP) is an uncommon fibroinflammatory pancreatic disorder that may closely mimic pancreatic malignancy, particularly when presenting with focal or multifocal mass-like lesions. Prompt recognition is essential to prevent unnecessary invasive procedures, inappropriate oncological management, and to allow timely initiation of glucocorticoid therapy. We report the case of a 32-year-old call center employee with a history of asthma who presented with a three-week history of progressive epigastric pain radiating to the back. Notably, he had no clinical or biochemical evidence of obstructive jaundice, with a total bilirubin level of 0.24 mg/dL at presentation. Initial abdominal CT demonstrated multifocal poorly defined hypovascular pancreatic lesions associated with pancreatic enlargement, raising concern for a pancreatic neoplasm. Laboratory evaluation revealed preserved hepatic function, normal serum calcium and triglyceride concentrations, mild inflammatory response, elevated total immunoglobulin G (IgG) (1673 mg/dL), mildly elevated IgG4 (153.5 mg/dL), and positive antinuclear antibodies. Tumour markers were negative. Subsequent MRI showed multifocal enlargement involving the pancreatic head, body, and tail, with delayed homogeneous enhancement, preservation of the main pancreatic duct calibre, and peripheral capsule-like features. These findings strongly suggested autoimmune pancreatitis. Histological confirmation was not initially obtained because corticosteroid therapy had already been initiated following multidisciplinary evaluation. The patient demonstrated rapid clinical improvement and remained asymptomatic during corticosteroid tapering. Endoscopic ultrasound-guided tissue acquisition and urgent imaging reassessment were planned to consolidate diagnostic certainty and exclude alternative diagnoses. This case highlights the diagnostic complexity of autoimmune pancreatitis presenting as multifocal pancreatic masses and illustrates the challenges associated with initiating corticosteroid therapy before histological confirmation. Recognition of characteristic radiological patterns and integration of clinical and serological findings remain crucial to avoid unnecessary invasive or surgical interventions.