Autoimmune pancreatitis

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Overview & Pathophysiology - Pancreas Under Fire

  • A chronic fibro-inflammatory process driven by immune dysregulation, often mimicking pancreatic cancer.
  • Two distinct subtypes:
    • Type 1 (Lymphoplasmacytic Sclerosing Pancreatitis): A manifestation of systemic IgG4-related disease (IgG4-RD). Typically affects males >60 years. Histology shows dense lymphoplasmacytic infiltrate, storiform fibrosis, and obliterative phlebitis.
    • Type 2 (Idiopathic Duct-Centric Pancreatitis): A pancreas-specific disorder strongly associated with IBD (UC > Crohn's). Not related to IgG4. Histology shows neutrophilic infiltration of the ductal epithelium (granulocytic epithelial lesions or GELs).

CT: Diffusely enlarged, hypoattenuating pancreas

⭐ Type 1 AIP characteristically presents with a diffusely enlarged, featureless, "sausage-shaped" pancreas on imaging and is highly responsive to steroid therapy.

Clinical Presentation & Diagnosis - The Great Pretender

  • Presents insidiously, often mimicking pancreatic cancer.
    • Painless obstructive jaundice (most common presentation).
    • Mild, recurrent abdominal pain or back pain; weight loss.
  • Two distinct types:
    • Type 1 (IgG4-related): Affects older males (>60), involves other organs (bile ducts, retroperitoneum, salivary glands), and shows ↑ serum IgG4.
    • Type 2 (Idiopathic Duct-Centric): Affects younger patients, is strongly associated with IBD (especially Ulcerative Colitis), and has normal IgG4 levels.
  • Key Investigations:
    • Imaging: Diffusely enlarged, "sausage-shaped" pancreas with a featureless border and a surrounding capsule-like rim on CT/MRI.
    • Serology: ↑ Serum IgG4 (>135 mg/dL) is highly suggestive of Type 1.

⭐ Often presents as painless obstructive jaundice, making it a key mimic of pancreatic adenocarcinoma. Biopsy is often required for differentiation.

  • Diagnosis: Based on 📌 HISORt criteria (Histology, Imaging, Serology, Other organ involvement, Response to therapy).

Histology & Types - Two Faces of Inflammation

Histology of Autoimmune Pancreatitis

FeatureType 1 AIP (LGPS)Type 2 AIP (IDCP)
HistologyLymphoplasmacytic Sclerosing Pancreatitis (LGPS); dense periductal lymphoplasmacytic infiltrate, storiform fibrosis, obliterative phlebitis.Idiopathic Duct-Centric Pancreatitis (IDCP); ductal neutrophilic infiltration (Granulocytic Epithelial Lesion - GEL), minimal fibrosis.
Serum IgG4↑↑ Elevated in >80%Normal
SystemicIgG4-Related Disease (IgG4-RD); affects bile ducts, salivary glands, kidneys.Pancreas-specific; rarely other organs.
AssociationIgG4-RDInflammatory Bowel Disease (IBD), esp. Ulcerative Colitis (~30%).
RelapseCommon post-steroidsRare

Treatment & Management - Cooling the Flames

  • Primary Goal: Induce remission, prevent relapse, and manage complications (e.g., biliary strictures).

Rituximab is increasingly used as a first-line agent for induction or for steroid-refractory/dependent disease, especially in Type 1 AIP, due to its high efficacy and steroid-sparing effects.

  • Often mimics pancreatic cancer but features a "sausage-shaped" pancreas on imaging and elevated serum IgG4 levels (in Type 1).
  • Type 1 is part of a systemic IgG4-related disease, affecting other organs like bile ducts and retroperitoneum.
  • Type 2 is pancreas-specific and strongly associated with inflammatory bowel disease (IBD), particularly ulcerative colitis.
  • Histology shows lymphoplasmacytic sclerosing pancreatitis (Type 1) or duct-centric inflammation (Type 2).
  • Hallmark feature is a dramatic response to corticosteroids.

Practice Questions: Autoimmune pancreatitis

Test your understanding with these related questions

A 35-year-old Caucasian female presents with anemia, malaise, bloating, and diarrhea. Past genetic testing revealed that this patient carries the HLA-DQ2 allele. The physician suspects that the patient's presentation is dietary in cause. Which of the following findings would definitively confirm this diagnosis?

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Flashcards: Autoimmune pancreatitis

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Chronic pancreatitis may present with _____, which results in malabsorption with steatorrhea and fat-soluble vitamin deficiences

TAP TO REVEAL ANSWER

Chronic pancreatitis may present with _____, which results in malabsorption with steatorrhea and fat-soluble vitamin deficiences

pancreatic insufficiency

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