Autoimmune pancreatitis (AIP) was initially recognized as a disease that primarily affects the pancreas with some ability to spread to other organs. More recently, there has been increasing recognition of the systemic association of AIP with a number of autoimmune conditions [1].

AIP can now be classified into type 1 and type 2, each presenting a distinct clinical profile. In type 1 AIP, the pancreas is a part of a systemic IgG4-positive disease, also known as lymphoplasmacytic sclerosing pancreatitis (LPSP). Type 1 AIP is a rare disease which is more prevalent in men, and typical patients are between ages 60 and 65 [2]. Diagnosis of type 1 AIP can follow several criteria—radiological, serological, histological, and clinical—that have been established internationally over time. Notable among these are the HISORt (histology, imaging, serology, other organ involvement, and response to therapy) criteria established by the Mayo clinic [3] and the more recent International Consensus Diagnostic Criteria (ICDC) guidelines [4].

The five features of the ICDC guidelines are similar to the criteria used in HISORt and include (1) pancreatic imaging of either the parenchyma or ducts, (2) serology, (3) other organ involvement (OOI), (4) histology of the pancreas, and (5) response to corticosteroid therapy. It is notable that type 1 AIP can be further classified into typical and atypical patterns based on the ICDC guidelines. While the typical pattern completely follows established ICDC guidelines, these criteria are not met in atypical type 1 AIP. For completing the diagnosis of atypical type 1 AIP, there is a requirement for an endoscopic pancreatogram and pancreatic biopsy.

Significant observations in type 1 AIP are diffuse enlargement of the pancreatic parenchyma on CT scan [5]. This is otherwise also visualized as a sausage-like pancreas. On endoscopic retrograde cholangiopancreatography (ERCP), one might observe long strictures or multiple strictures of the pancreatic duct [6]. IgG4 serum levels in type 1 AIP can be up to ten times the upper limit of IgG4 values [5]. Histologic findings can include marked lymphoplasmacytic infiltration with fibrosis (without granulocytic infiltration), storiform fibrosis, obliterative phlebitis, and abundant (>10 cells/HPF) IgG4-positive cells [5].

Type 2 AIP is of idiopathic origin and manifests as a duct-centric pancreatitis. Patients with type 2 AIP tend to be younger (aged 45–48), and there is an equal distribution across gender [7]. Serologic changes in IgG4 are absent in type 2 AIP. In addition, the pathology of type 2 AIP is idiopathic and restricted to the pancreas (head and distal portion of the bile duct) with no demonstrable extra-pancreatic involvement. Histologically, type 2 AIP is associated with granulocytic epithelial lesions (GELs). However, GELs are likely to be present in 27% of type 1 AIP cases [8]. In addition, due to the lack of OOI and IgG4 in type 2 AIP, which indicates a systemic autoimmune process, there is a need for pancreatic biopsy to rule out pancreatic cancer prior to establishing the diagnosis of AIP [9].

The classic clinical presentation of the AIPs involves obstructive jaundice, abdominal pain, and acute pancreatitis [7]. Obstructive jaundice is a common presenting symptom, more so in type 1 than in type 2 AIP. Thus, patients may require the placement of a biliary stent while they await diagnostic confirmation for alleviation of the symptoms. Abdominal pain experienced in AIP is mild and may or may not be accompanied by attacks of abdominal pain from acute pancreatitis. In the later stages, patients with AIP may develop severe exocrine and endocrine insufficiency [10]. In addition, untreated type 1 AIP can manifest as systemic inflammation showing sclerosing cholangitis, thyroiditis, lymphadenopathy, sialadenitis, and retroperitoneal fibrosis [11].

The presenting symptoms in AIP are largely similar to those that manifest in pancreatic adenocarcinoma. It is essential to rule out adenocarcinoma and multiple tests can be used to this end. CA 19-9 levels can be elevated in AIP and in pancreatic adenocarcinoma due to bile duct obstruction. However, the levels of CA 19-9 should drop with a trial of steroids for the treatment of AIP. CA 19-9 levels that continue to rise are a red flag for the presence of a pancreatic cancer [12]. A FNA or core biopsy of the pancreas could yield some evidence, and surgical resection is necessary for confirmation.

The management of AIP involves the oral administration of glucocorticoids (prednisone and prednisolone are commonly used). The standard dose of corticosteroids to be given for AIP is 40 mg of prednisone for 4 weeks. A reassessment of imaging and laboratory work is recommended after 2 weeks. Tapering of the corticosteroids can be done at the rate of 5 mg/day every week for 8 weeks. Successful treatment involves the resolution of clinical symptoms and downward trending of CA 19-9, IgG4, and liver function tests.