Autoimmune pancreatitis (AIP) is a form of chronic pancreatitis characterized by a diffuse enlargement of the pancreas, narrowing of the pancreatic duct, lymphoplasmacytic infiltration and fibrosis, increased serum IgG4 and response to steroid treatment.

Epidemiology

• Incidence - rare, 5-6% of patients with chronic pancreatitis
• Age - most are >50 years at onset
• Gender - More prevalent in males than females

Pathophysiology

• Histologic hallmark is collar-like preductal infiltrates composed of lymphocytes and plasma cells termed lymphoplasmacytic sclerosing pancreatitis (LPSP)
  • Other organs may be involved including the gallbladder, bile ducts, kidney, lung and salivary glands
  • IgG4 positive plasma cells have been identified in some patients

Clinical Presentation

• AIP may coexist in about 40-60% of patients with autoimmune diseases such as Sjögren’s syndrome, primary sclerosing cholangitis (PSC) and primary biliary cirrhosis (PBC), suggesting that common targets in the pancreas or exocrine organs such as the salivary gland or biliary tract may be involved in disease pathogenesis
• Pancreatic
  • Obstructive jaundice
  • Abdominal pain
  • Diabetes
  • Weight loss
• Extrapancreatic
  • Pulmonary - discrete nodules, diffuse infiltrate, hilar adenopathy
  • Renal - lesions, mild renal insufficiency

Treatment

• Steroids
  • Positive response to steroids confirms diagnosis

Diagnosis

• No consensus diagnostic criteria for autoimmune pancreatitis has been established
• Current diagnostic criteria for autoimmune pancreatitis includes the following:
  • Diagnostic criteria for autoimmune pancreatitis by the Japan Pancreas Society
  • Kim diagnostic criteria for autoimmune pancreatitis (Korea)
  • HISORt diagnostic criteria for autoimmune pancreatitis (Mayo, USA)
  • Diagnostic criteria for autoimmune pancreatitis by the Italian group
• Although significant differences exist between these criteria, overlaps occur in certain aspects
• The most comprehensive diagnostic criteria is that from the Japanese group
  • The Japanese diagnostic criteria for AIP require the presence of imaging together with a laboratory and/or a histopathological finding

• Laboratory Testing
  • IgG, IgG4 testing
  • Consider autoantibodies testing
    • Antilactoferrin (ALA), anti-carbonic anhydrase (ACA), antismooth muscle (ASMA), antinuclear antibodies (ANA)
• Histology
  • Characterized by lymphocyte and plasma cell infiltration
  • Important in differentiating AIP from acute and chronic pancreatitis, lymphoma and pancreatic cancer
• Imaging studies
  • Ultrasound/CT/MRI
  • Endoscopic retrograde cholangiopancreatography (ECRP)

Differential Diagnosis

• Pancreatic or biliary cancer
  • Primary sclerosing cholangitis (PSC)
  • Primary biliary cirrhosis (PBC)
  • Inflammatory bowel diseases (ulcerative colitis, Crohn’s disease)
  • Sjögren syndrome
  • Rheumatoid arthritis
  • Autoimmune thyroid diseases