Introduction
Autoimmune pancreatitis (AIP) is a rare, immune-mediated form of chronic pancreatitis, classified into three subtypes. Type 1 AIP, the pancreatic manifestation of IgG4-related disease, often presents with multisystem involvement and frequent relapse (1,2). Type 2 AIP is pancreas-limited, tends to affect younger individuals, and is commonly associated with inflammatory bowel disease (IBD) (2,3). A third form—checkpoint inhibitor-related pancreatitis (CIP or Type 3 AIP)—has been recently described in patients receiving immune checkpoint inhibitors, typically asymptomatic but may result in pancreatic atrophy (4).
Precise subtyping is critical due to differences in clinical behavior, relapse risk, and treatment response (1,2,3). We present a single-center series comparing clinical, radiologic, and histopathologic characteristics of Type 1 and Type 2 AIP.
Aims & Methods
We retrospectively reviewed 20 patients diagnosed with AIP between 2020–2024 at a tertiary center. Classification followed International Consensus Diagnostic Criteria (1). Diagnostic evaluation included endoscopic ultrasound (EUS), serum IgG4 levels, and contrast-enhanced CT/MRI/MRCP (1,2). EUS-guided fine-needle biopsy (FNB) was performed where malignancy could not be excluded. Histopathology differentiated lymphoplasmacytic sclerosing pancreatitis (LPSP, Type 1) from idiopathic duct-centric pancreatitis (IDCP, Type 2) (2). Data on extra-pancreatic involvement, steroid response, and relapse were collected.
Results
Fifteen patients were diagnosed with Type 1 AIP and five with Type 2. Type 1 patients had a mean age of 63 years and were predominantly male (80%). Obstructive jaundice was the most common presentation. All had elevated serum IgG4. EUS revealed diffusely hyperechoic parenchyma and long-segment ductal narrowing. Histology confirmed LPSP. Extra-pancreatic involvement was observed in 60%, most commonly IgG4 cholangitis. All responded to corticosteroids; 40% relapsed within one year and received rituximab (5).
Type 2 patients had a mean age of 38, with equal gender distribution. Presenting symptoms included abdominal pain and acute pancreatitis. Serum IgG4 was normal in all cases. EUS revealed focal hypoechoic lesions with short-segment narrowing. Histology confirmed IDCP. Two patients (40%) had ulcerative colitis. All achieved remission with steroids, and no relapses were observed (2,3).
Conclusion
This series emphasizes the distinct clinical courses of AIP subtypes. Type 1 AIP represents a systemic IgG4-related disease with high relapse risk, often requiring long-term immunosuppression (5). Type 2 AIP affects younger patients, remains confined to the pancreas, and shows sustained remission after steroid therapy (2,3). Accurate classification using EUS, MRCP, IgG4, and histology is crucial for appropriate management and long-term outcomes (1,2).
References
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