Granulomatosis with Polyangiitis Presenting as Pancreatic Pseudotumor and Peripancreatic Lymphadenitis: Diagnostic Challenges and Review of 55 Cases.

BACKGROUND The spectrum of anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) encompasses granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). These pathologies predominantly affect small to medium-sized vessels, with frequent involvement of the ear, nose, and throat (ENT) sphere, lungs, and kidneys. Pancreatic involvement, an exceedingly rare manifestation of AAV, manifests as pancreatitis, a pancreatic mass, or a cystic lesion. This study reports a new case of pancreatic GPA and reviews the literature to characterize its clinical, radiological, and histological features. CASE REPORT A 54-year-old woman with severe epigastric pain, vomiting, and weight loss presented with a pancreatic mass and peripancreatic lymphadenitis on imaging studies, raising high suspicion for cancer. Repeated endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) biopsies were inconclusive. Distal pancreatectomy with splenectomy was performed. Histopathology demonstrated granulomatous inflammation with necrosis and vasculitis, and anti-PR3 ANCA testing was positive. A diagnosis of GPA was made and treatment with corticosteroids and rituximab resulted in clinical remission. We identified 54 additional cases of pancreatic AAV in the literature and analyzed their clinical features. CONCLUSIONS In cases of unexplained pancreatitis or pancreatic masses/pseudocysts, AAV should be considered. A targeted evaluation - including ANCA testing, imaging, biopsies, and a systematic search for ENT, lung, kidney, and skin manifestations - is essential to identify key clinical, serological, and radiological clues of pancreatic AAV. We propose to classify this as type 4 autoimmune pancreatitis. A corticosteroid-based regimen, with or without additional immunosuppressants, offers effective disease control, making pancreatic surgery unnecessary.