Diagnosis

Autoimmune pancreatitis is difficult to diagnose, because its signs and symptoms are very similar to those of pancreatic cancer. However, an accurate diagnosis is extremely important. Undiagnosed cancer may result in delaying or not receiving necessary treatment.

People with AIP tend to have a general enlargement of the pancreas, but they may also have a mass in the pancreas. To pinpoint the diagnosis and determine which type of AIP you have, blood and imaging tests are necessary.

Tests

No single test or characteristic feature identifies autoimmune pancreatitis. Consensus guidelines for diagnosis use a combination of imaging, blood tests and biopsy results.

Specific tests may include:

• Imaging tests. Tests of your pancreas and other organs may include CT, MRI, endoscopic ultrasound (EUS) and endoscopic retrograde cholangiopancreatography (ERCP).

• Blood tests. You will be tested for elevated levels of an immunoglobulin called IgG4, produced by your immune system. People with type 1 AIP, but usually not with type 2 AIP, will have highly elevated blood levels of IgG4.

  However a positive test doesn't necessarily mean that you have the disease. A small number of people who don't have autoimmune pancreatitis, including some with pancreatic cancer, also have high blood levels of IgG4.

• Endoscopic core biopsy. In this test, pathologists analyze a sample of pancreatic tissue in the laboratory. AIP has a distinctive appearance that can be easily recognized under a microscope by an expert pathologist. Doctors insert a small tube (endoscope) through the mouth into the stomach and, guided by ultrasound, remove some tissue from the pancreas using a special needle.

  The challenge is obtaining a sample of tissue large enough to analyze, rather than just a few cells. This procedure is not widely available, and results may not be conclusive.

• Steroid trial. Autoimmune pancreatitis generally responds to steroids; doctors sometimes use a trial course of this drug to confirm a diagnosis. However, this strategy should ideally be under expert guidance, be used sparingly and only be done when there is strong evidence to support a diagnosis of autoimmune pancreatitis. Response to corticosteroids is measured by CT and improvement in serum IgG4 levels.