Autoimmune pancreatitis (AIP) can be particularly challenging to diagnose because the way it presents itself closely resembles pancreatic cancer. The most common sign, present in about 80 percent of people, is painless jaundice, caused by blocked bile ducts. AIP can also cause weight loss. Masses in the pancreas and other organs of many people with autoimmune pancreatitis can be misdiagnosed as cancer.
Pancreatic specialists at Mayo Clinic are leading efforts to standardize diagnostic guidelines so that the disorder can be consistently and correctly identified and unnecessary surgery avoided.
No single test or characteristic feature identifies autoimmune pancreatitis. Mayo's approach to diagnosis comprises the following:
- Imaging tests. Imaging of the pancreas and other organs is usually the first step in diagnosis. Mayo Clinic radiologists have extensive experience evaluating autoimmune pancreatitis using advanced technologies, such as dual-phase helical CT scans and MRI, which produce superior images of the pancreas, bile ducts and liver. It is essential to have images read by radiologists with expertise in pancreatic disorders.
- Blood tests. Elevated levels of an antibody called IgG4 are a common feature of autoimmune pancreatitis. These antibodies are produced by your immune system. But a positive test doesn't mean that you have the disease. Studies at Mayo Clinic have shown that a small number of people who don't have autoimmune pancreatitis, including some with pancreatic cancer, also have high blood levels of IgG4 antibodies.
- Endoscopic core biopsy. Pathologists analyze a sample of pancreatic tissue in the laboratory to help confirm the diagnosis of autoimmune pancreatitis. The disease has a distinctive appearance that is easily recognized under a microscope. The challenge is obtaining a sample of whole tissue large enough to analyze. Mayo Clinic specialists are often able to get a suitable sample by inserting a small tube (endoscope) through the mouth into the stomach and, guided by ultrasound, removing some tissue from the pancreas (biopsy) using a special needle. Mayo Clinic is one of the few medical centers in the world performing core biopsies of the pancreas.
- Steroid trial. Because autoimmune pancreatitis is the only pancreatic disorder known to respond to corticosteroids, Mayo doctors sometimes use a trial course of this drug to confirm a diagnosis. If your signs and symptoms improve — for instance, your IgG4 level drops or a mass in your pancreas shrinks — you are considered to have autoimmune pancreatitis. However, this approach should be used only by doctors thoroughly familiar with the disease, as steroids give a general feeling of well-being even in people with cancer. Also, elevation of IgG4 not associated with AIP may also decrease with steroid use, giving a false sense of reassurance.