Autoimmune Pancreatitis

There are two types of autoimmune pancreatitis: type 1 and type 2. They have some similarities, but they affect people differently and have different risks of relapse and other health conditions.

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Type 1 AIP

Type 1 AIP is the pancreatic form of  IgG4-related disease (IgG4-RD), a condition that can also affect other organs, including the bile ducts, kidneys, salivary glands, lymph nodes, and liver.

• Who it affects: More common in men and usually develops after age 60.
• Other Conditions: May occur with IgG4-related disease affecting other organs.
• Chance of relapse: Higher risk of relapse after treatment.

Type 2

Usually affects the pancreas only.

• Who it affects: Affects men and women more equally and tends to develop at a younger age.
• ‍Other Conditions: Often associated with inflammatory bowel disease (IBD), particularly ulcerative colitis.
• Chance of relapse: Lower risk of relapse after treatment.

Remember: Type 1 and Type 2 AIP are different diseases. Type 1 AIP is associated with IgG4-related disease, while Type 2 AIP is not.

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What is IgG4?  

IgG4 is a type of antibody made by the immune system. It normally helps regulate immune responses and is found in small amounts in the blood. In some people, an abnormal immune response involving IgG4 can contribute to IgG4-related disease (IgG4-RD).

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IgG4-RD is a rare, chronic immune-mediated condition that can cause inflammation and tissue changes in one or more organs. It can affect different parts of the body, sometimes at the same time.

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In people with IgG4-RD, IgG4-producing immune cells can become overactive and accumulate in affected tissues, causing inflammation and, over time, scarring.

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A blood test can measure the IgG4 level, but an elevated level does not by itself mean someone has IgG4-RD. Some people with IgG4-RD have normal blood IgG4 levels, and elevated IgG4 can occur with other conditions. Doctors use a combination of symptoms, imaging, blood tests, and sometimes a biopsy to make the diagnosis.

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IgG4-RD is generally treatable, particularly when recognized early. Corticosteroids are commonly used initially to control inflammation, although some people need additional treatment to maintain remission.

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AIP can be difficult to recognize because some people have few or no symptoms. When symptoms occur, they may include:

• Yellowing of the skin or eyes (jaundice), which may be painless  
• Dark urine  
• Pale stools  
• Pain in the upper abdomen or middle of the back  
• Nausea or vomiting  
• Loss of appetite  
• Fatigue  
• Unexplained weight loss

Type 1 AIP commonly causes jaundice when inflammation blocks or narrows the bile ducts. Type 2 AIP may instead cause repeated episodes of acute pancreatitis.

AIP is genuinely difficult to diagnose because it is a rare disease and symptoms can mimic pancreatic cancer and getting it right matters, since misdiagnosed cancer can mean dangerous treatment delays. There's no single diagnostic test; in the appropriate clinical context, doctors need to combine imaging, blood work, and often biopsy results.

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Is Autoimmune Pancreatitis the Same as Pancreatic Cancer?

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No. Autoimmune pancreatitis is not pancreatic cancer.

However, AIP can sometimes look like pancreatic cancer on imaging tests, and the symptoms can be similar. For this reason, getting an accurate diagnosis is very important. Treating AIP as cancer—or missing cancer because it is mistaken for AIP—can have serious consequences.

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Doctors may need several tests to distinguish AIP from pancreatic cancer and other pancreatic conditions.

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What Causes Autoimmune Pancreatitis?

The exact cause of AIP is not known. Researchers believe that the immune system mistakenly targets healthy tissue in the pancreas, causing inflammation.

Type 1 AIP is part of IgG4-RD, a condition that can cause inflammation in several organs throughout the body. Type 2 AIP is often associated with inflammatory bowel disease, particularly ulcerative colitis.

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Tests Your Doctor May Use

• Imaging tests: CT, MRI, endoscopic ultrasound (EUS), or ERCP to look at the pancreas and nearby organs.
• Blood tests: checking for elevated blood IgG4, an immune protein. Type 1 AIP usually shows very high IgG4 levels; type 2 usually does not. (Note: a small number of people without AIP — including some with pancreatic cancer — can also have high IgG4, so this test alone isn't definitive.)
• Endoscopic core biopsy: a small tissue sample is taken from the pancreas or bile duct using a needle guided by ultrasound, through an endoscope passed via the mouth. AIP has a distinctive look under the microscope, but getting enough tissue can be challenging, and this test isn't available everywhere.
• Steroid trial: since AIP typically responds well to steroids, doctors sometimes use a short treatment trial course with steroids to help confirm the diagnosis — but only under expert guidance and when there's already strong evidence pointing to AIP.

• Biliary Stenting: If jaundice is present from a blocked bile duct, doctors may place a small tube (stent) to drain it before starting medication. Often, though, jaundice improves with steroids alone. The endoscopic procedure to place the stent may also help confirm the diagnosis by allowing doctors to collect tissue samples during stent placement.
• Steroids: Steroids, such as prednisone or prednisolone, are the main first line of treatment for AIP, and most people respond quickly. Lack of response to steroids should make clinicians reconsider the diagnosis.
• Immunosuppressants and Other Immune-Targeted Treatments: AIP can sometimes come back after treatment. If it relapses, your doctor may recommend a steroid-sparing medication. These may include azathioprine, mycophenolate, mercaptopurine, or rituximab. For adults with IgG4-RD, newer targeted treatments may also be an option. Your doctor will consider your symptoms, other organs affected by IgG4-related disease, previous treatments, and risk of relapse when choosing the best treatment.

Because type 1 AIP can affect other organs, including lymph nodes, salivary glands, bile ducts, liver, and kidneys, regular follow-up is important even after symptoms improve.

AIP can relapse, meaning that inflammation returns after treatment.

Relapse is more common with type 1 AIP than type 2. People with type 1 AIP may need longer-term monitoring and, in some cases, additional treatment to prevent or manage relapses.  

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If you have been treated for AIP, follow-up appointments are important even if you are feeling better.

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What Are the Possible Complications?

AIP can affect how well the pancreas works. Possible complications include:

• Exocrine pancreatic insufficiency (EPI), in which the pancreas does not make enough digestive enzymes, making it harder to digest food and absorb nutrients
• Diabetes, if the pancreas is unable to produce enough insulin
• Narrowing or blockage of the bile ducts
• Pancreatic calcifications or stones

Treatment itself, particularly long-term steroid treatment, can also cause side effects. Your healthcare team can monitor you and adjust your treatment as needed.  

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When Should I Contact a Doctor?

Talk with your healthcare provider if you develop yellowing of the skin or eyes (jaundice), unexplained weight loss, persistent abdominal or back pain, or symptoms of pancreatitis. Because AIP can have symptoms similar to other pancreatic conditions, including pancreatic cancer, these symptoms should be evaluated by a healthcare professional.