Type 1 AIP is now regarded as a manifestation of IgG4-related disease,[2] and those affected have tended to be older and to have a high relapse rate.

Type 1 pancreatitis, is as such as manifestation of IgG4 disease, which may also affect bile ducts in the liver, salivary glands, kidneys and lymph nodes.

Two-thirds of patients present with either painless jaundice due to bile duct obstruction or a "mass" in the head of the pancreas, mimicking carcinoma.

At the initial stages, typically, there is a cuff of lymphoplasma cells surrounding the ducts but also more diffuse infiltration in the lobular parenchyma.

Whereas histopathologic examination remains the primary method for differentiation of AIP from acute and chronic pancreatitis, lymphoma, and cancer.

[5] Although the exact mechanism explaining the clinical manifestations of autoimmune pancreatitis remain for an important part obscure, most professionals would agree that the development of IgG4 antibodies, recognizing an epitiope on the membrane of pancreatic ancinar cells is an important factor in the pathophysiology of the disease.

These antibodies are postulated to provoke an immune response against these ancinar cells resulting in pancreatic inflammation and destruction.

[11] Computed tomography (CT) findings in AIP include a diffusely enlarged hypodense pancreas or a focal mass that may be mistaken for a pancreatic malignancy.

[8] A low-density, capsule-like rim on CT (possibly corresponding to an inflammatory process involving peripancreatic tissues) is thought to be an additional characteristic feature (thus the mnemonic: sausage-shaped).

Magnetic resonance imaging (MRI) reveals a diffusely decreased signal intensity and delayed enhancement on dynamic scanning.

The failure to differentiate AIP from malignancy may lead to unnecessary pancreatic resection, and the characteristic lymphoplasmacytic infiltrate of AIP has been found in up to 23% of patients undergoing pancreatic resection for suspected malignancy who are ultimately found to have benign disease.

However, accurate and timely diagnosis may preempt the misdiagnosis of cancer and decrease the number of unnecessary pancreatic resections.

There are also a large number of case reports employing descriptive terminology such as pancreatitis associated with Sjögren's syndrome, primary sclerosing cholangitis, or inflammatory bowel disease.