Autoimmune Pancreatitis

Background

• Autoimmune pancreatitis (AIP) is the pancreatic manifestation of IgG4-related disease.
• There are 2 clinical and pathological subtypes of AIP.
• In type 1 AIP:
  • abdominal pain is usually absent
  • extrapancreatic lesions, such as sclerosing cholangitis, sclerosing sialadenitis, and retroperitoneal fibrosis are often seen
  • serological abnormalities are often seen, such as elevated IgG4
  • histology is characterized by lymphoplasmacytic infiltrate and fibrosis
• In type 2 AIP:
  • abdominal pain is common
  • there are no serological biomarkers
  • usually only the pancreas is involved
  • histology identifies granulocyte epithelial lesions, the presence of intraluminal and intraepithelial neutrophils in small- and medium-sized ducts, with no or very low number of IgG4-positive plasma cells

Evaluation

• Diseases that may mimic AIP should be considered first and excluded, including:
  • pancreatic cancer
  • sclerosing cholangitis
  • cholangiocarcinoma
  • hepatocellular carcinoma
• Painless jaundice is the most common presenting symptom, other signs and symptoms may include:
  • acute pancreatitis
  • abdominal pain with characteristics of pancreatitis
  • back pain
  • weight loss
  • steatorrhea
  • acute cholangitis
• In patients suspected of AIP, the diagnosis is made by application of the HISORt criteria that incorporates findings on Histology, Imaging, Serology, Other organ involvement, Response to Therapy criteria for autoimmune pancreatitis.
• It is common that in patients suspected of AIP, multiple imaging modalities may be required, as CT, MRI, endoscopic ultrasound. ERCP may be particularly useful in assessment of pancreatic and biliary strictures.
• Serum IgG4 may be elevated in patients with IgG-4 related disease, but its elevation cannot exclude other diagnoses.
• The combination of Ca 19-9 < 74 units/mL and IgG4 > 1 mg/dL may be useful in diagnosis as one study found it had positive predictive value 100% and negative predictive value 96% for AIP.

Management

• Corticosteroids are first line therapy.
• Although optimal dosing and duration unknown, high dose prednisone is commonly used (30-40 mg/day for 3-4 weeks).
• In diabetics and older patients, lower dose prednisone (0.6 mg/kg/day for 2-4 weeks) may be used.
• For maintenance of remission, consider prolonged prednisone taper over several months or years.
• In event of relapse, consider high-dose corticosteroid regimen with or without subsequent corticosteroid maintenance.
• In patients intolerant of corticosteroids or with refractory disease, consider
  • immunomodulators
    • azathioprine
    • mycophenolate mofetil
    • methotrexate
    • sirolimus
  • rituximab