Autoimmune pancreatitis (AIP)

Discuss AIP?
Autoimmune pancreatitis (AIP) is a rare disorder of presumed autoimmune aetiology that is associated with characteristic clinical, histologic, and morphologic findings. It is not common in western countries. The mean age of diagnosis is 55, this however can vary with cases presenting from 30 to 70 years of age. A male predilection of has been reported.

Discuss the clinical features of AIP?

These include mild, acute recurrent pancreatitis, biliary and pancreatic duct strictures with a
clinical presentation resembling PSC, and a pancreatic mass that can be confused with pancreatic carcinoma or lymphoma.
AIP can coexist with a variety of other conditions including IBD (primarily ulcerative colitis), Sjögren’s syndrome, lung nodules (and adenopathy and infiltrates), and retroperitoneal fibrosis.
Diagnostic criteria proposed by the Mayo Clinic include the presence of ≥1 of the following:

  • Diagnostic histology (Marked lymphoplasmacytic infiltration and dense fibrosis)
  • Characteristic imaging on computed tomography and pancreatography with elevated serum IgG4 levels.
  • Response to steroid therapy of pancreatic/extrapancreatic manifestations

Discuss the diagnosis of AIP?

  • Diagnostic imaging plays a critical role in the diagnosis of autoimmune pancreatitis. It is often the first investigative modality that raises the possibility of autoimmune pancreatitis, based on characteristic imaging features. Characteristic findings on CT include diffusely enlarged pancreas, commonly referred to as ‘sausage-like’ or ‘bulky’, minimal peri-pancreatic fat infiltration and lack of pancreatic parenchymal calcification. Focal involvement typically appears as a mass, most commonly involving the head of the pancreas, with low attenuation. Similar features are seen on MRI.
  • ERCP or MRCP may reveal a narrowed main and dorsal pancreatic duct; diffuse, irregular narrowing of the pancreatic duct (beaded appearance), or a focal stricture of the pancreatic duct, proximal or distal common bile duct; or irregular narrowing of the intrahepatic ducts. A stricture in the common bile duct or the finding of a lesion in the head of the pancreas often prompts consideration of malignancy.
  • Elevated serum levels of IgG4 provide a marker for the disease.   However, IgG4 levels in AIP may not be universally elevated (at least at initial presentation) and levels can also be elevated in other conditions.
  • Thus, neither imaging tests nor the serum IgG4 level is usually sufficient for establishing a firm diagnosis, which requires a pancreatic biopsy.

Discuss the treatment of AIP?
AIP can respond dramatically to steroids. The rate of response is variable (typically one to four months).  The optimal dose and duration have not been established. Prednisolone at a dosage of 0.5mg/kg/day for 2-3 months followed by a taper of 5 mg/week is usually used. Repeat imaging and IgG4 levels are done at 4-6 weeks to assess response.  Failure to respond in this time-frame should raise the possibility of alternative diagnoses.
Patients who relapse upon discontinuation of steroids can be managed with a repeat course and/or maintenance therapy aiming for the minimum dose in which a response is maintained.

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