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Autoimmune pancreatitis (AIP) is a unique form of chronic pancreatitis caused by an immune-mediated inflammatory process. It represents the pancreatic manifestation of IgG4-related systemic disease and is characterized by lymphoplasmacytic infiltration, fibrosis, and responsiveness to corticosteroid therapy.

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Etiopathogenesis

• Immune-mediated: Thought to be secondary to abnormal activation of T-lymphocytes and elevated serum IgG4 levels.
• Types:
  • Type 1 AIP (IgG4-related disease) – associated with systemic involvement (sclerosing cholangitis, retroperitoneal fibrosis, renal lesions).
  • Type 2 AIP – pancreas-limited, usually IgG4 negative, associated with inflammatory bowel disease (especially ulcerative colitis).

Clinical Presentation

• Painless obstructive jaundice (most common presentation).
• Mild abdominal pain (unlike classical acute pancreatitis).
• Weight loss, new-onset diabetes, steatorrhea.
• Often mimics pancreatic adenocarcinoma, making diagnosis challenging.

Diagnostic criteria

International Consensus Diagnostic Criteria (ICDC):

• Imaging findings (CT/MRI/ERCP).
• Serology (raised IgG4).
• Histology (lymphoplasmacytic infiltration, storiform fibrosis).
• Other organ involvement (e.g., bile duct, kidneys).
• Response to steroids.

Radiology