Autoimmune Pancreatitis

Diagnosis

Mayo Clinic doctors use several tools to diagnose autoimmune pancreatitis (AIP) including imaging, endoscopic ultrasound-guided core biopsy, and blood testing. A core biopsy allows examination of pancreatic tissue without surgery. Mayo Clinic is one of a few medical centers with this capability.

Imaging

Imaging is usually done with computed tomography (CT) scans. Another test sometimes used is an endoscopic retrograde cholangiopancreatogram (ERCP). Doctors gently thread an endoscope down the throat and through the stomach to the opening of the bile and pancreatic ducts in the duodenum. A dye passed through a thin, flexible tube (catheter) inside the endoscope allows X-ray images of the ducts to be taken.

While there can be considerable variation in the appearance of the pancreas in patients with AIP, two patterns radiologists look for are:

• "Sausage-shaped" enlarged pancreas
• Lack of enlargement of the main pancreatic duct, a feature commonly seen in pancreatic cancer. An ERCP will show a diffusely narrow, irregular pancreatic duct.

Endoscopic Ultrasound-Guided Core Biopsy

Pathologists can diagnose AIP by examining pancreatic tissue because it has a very characteristic appearance under the microscope, with an abundance of plasma cells containing the subclass 4 of immunoglobulin G (IgG4). However, pathologists need at least a small piece of whole tissue to make the diagnosis. Pancreatic biopsy using endoscopic ultrasound (EUS) guidance is a key tool in diagnosing AIP. Doctors insert an endoscope into the digestive tract and ultrasound images help guide removal of a cylindrical (core) tissue sample from the pancreas using a hollow needle. The procedure is similar to fine-needle aspiration (FNA). But while FNA collects cells by aspiration (suction), the EUS biopsy collects tissue by using a larger needle with a tiny spring-powered sliding tray inside. The procedure is sometimes called a Tru-cut biopsy (referring to the manufacturer's name for the special needle).

Pathologists examine the tissue, looking for characteristic accumulation of lymphocytes and plasmacytes and fibrosis (collection of tough fibers) around ducts and veins. Tissue from the Tru-cut biopsy can also be stained to identify an abundance of IgG4 positive plasma cells.

Blood Testing

Serum levels of the antibody of subclass 4 of immunoglobulin G (IgG4) are characteristically elevated in AIP. However, a recent Mayo Clinic study found that elevated levels of IgG4 are seen in a small proportion of patients without AIP, including some with pancreatic cancer. Therefore, elevated IgG4 levels alone are not sufficient to diagnose AIP.

Other Organ Involvement

Doctors may also look for signs of autoimmune response in other parts of the body such as:

• Fibrosis in the retroperitoneum (area containing the kidneys, aorta, renal tract and other structures)
• Narrowing of bile ducts in the liver
• Enlargement of the salivary glands
• Involvement of kidneys sometimes leading to kidney failure

Biopsies may also be taken from other organs to look for accumulation of lymphocytes and plasmacytes and elevated IgG4 levels.

Steroid Therapy

Because AIP is the only pancreatic disorder known to respond to steroids, steroid therapy may be used to confirm diagnosis in patients who (1) have elevated IgG4 levels but whose imaging and biopsy results are inconclusive and (2) in whom cancer and other causes of pancreatic disorder have been thoroughly investigated and excluded.