IgG4-unrelated type 1 autoimmune pancreatitis

Area of Science:

• Gastroenterology
• Immunology
• Endocrinology

Background:

• Autoimmune pancreatitis (AIP) is a chronic inflammatory condition often associated with elevated serum IgG4 levels and IgG4-positive plasma cell infiltration.
• Type 1 AIP is characterized by systemic involvement and a characteristic response to steroid therapy.

Observation:

• A 50-year-old male presented with hyperproteinemia, elevated hepatobiliary enzymes, and renal dysfunction.
• Fluorodeoxyglucose positron emission tomography revealed increased uptake in the pancreas, lacrimal and salivary glands, lymph nodes, and kidneys.
• Imaging showed pancreatic head swelling and bilateral kidney enlargement, with biliary and pancreatic duct strictures.

Findings:

• Despite markedly high immunoglobulin G (IgG) levels, serum IgG4 was not elevated, and histological examination revealed lymphoplasmacytic sclerosing pancreatitis without IgG4-positive plasma cells.
• The patient was diagnosed with type 1 AIP based on the International Consensus Diagnostic Criteria.
• Symptoms and laboratory abnormalities improved significantly following steroid treatment.

Implications:

• This case demonstrates that type 1 AIP can manifest without the typical IgG4 elevation or IgG4-positive plasma cell infiltration.
• AIP phenotypes may present heterogeneously, suggesting that IgG4 is not a mandatory diagnostic marker for all cases.
• Clinical and imaging findings, alongside response to steroids, remain crucial for diagnosing type 1 AIP, even in atypical serological presentations.