Autoimmune pancreatitis is a rare disorder of presumed autoimmune causation with characteristic chemical, histologic, and morphologic findings. It is referred to by various names, including nonalcoholic destructive pancreatitis, tumefactive pancreatitis, and sclerosing pancreatitis, depending in part on specific pathologic findings and on the presence of extrapancreatic manifestations. However, it is believed that the pathologic heterogeneity may reflect different stages or manifestations of the same disease.

Autoimmune pancreatitis has been described as a primary pancreatic disorder and is also associated with other disorders of presumed autoimmune etiology, including primary sclerosing cholangitis, primary biliary sclerosis, retroperitoneal fibrosis, rheumatoid arthritis, and Sjögren syndrome. As a result, it has been proposed that autoimmune pancreatitis represents a systemic autoimmune disease.

A. Symptoms and Signs

Mild symptoms, usually abdominal pain, are present but attacks of acute pancreatitis are unusual. Furthermore, autoimmune pancreatitis is not a common cause of idiopathic recurrent pancreatitis. In the United States, 50–65% of patients with autoimmune pancreatitis present with obstructive jaundice. Weight loss and new onset of diabetes may also occur. Patients who have associated autoimmune conditions have corresponding clinical features. In this regard, Sjögren syndrome, rheumatoid arthritis, retroperitoneal fibrosis, ulcerative colitis, autoimmune thyroiditis, tubulointerstitial nephritis, and mediastinal adenopathy have all been reported in patients with autoimmune pancreatitis (Tables 28–1 and 28–2).

B. Laboratory Findings

An obstructive pattern on liver tests is common (ie, disproportionately elevated serum alkaline phosphatase and minimally elevated serum aminotransferases). Elevated serum levels of (IgG₄ provide a marker for the disease, particularly in Western populations. Serum IgG₄ normally accounts for only 5–6% of the total IgG₄ in healthy patients but is elevated in those with autoimmune pancreatitis.

A large study compared serum IgG₄ levels in 20 patients diagnosed with autoimmune pancreatitis based on clinical features and response to corticosteroids with 20 age- and sex-matched controls and 104 patients with pancreatic cancer, chronic pancreatitis, primary biliary sclerosis, primary cholangitis, and Sjögren syndrome. The median serum IgG₄ concentration in the patients with autoimmune pancreatitis was 663 mg/dL compared with 51 mg/dL in healthy controls (in whom normal values ranged from 8 to 140 mg/dL). Using a cutoff of 280 mg/dL, the sensitivity and specificity of the serum IgG₄ value for distinguishing autoimmune pancreatitis from pancreatic cancer was 95–97%.

It has also been demonstrated that IgG₄ levels may decline during treatment with corticosteroids, and this can be used as a parameter to follow the response of patients to such therapy. These and other observations suggest that serum levels of IgG₄ may be useful to distinguish autoimmune pancreatitis from pancreatic cancer. Additionally, other antibodies such as antinuclear antibodies and rheumatoid factor may be present.

A serologic marker has been identified that is present in most patients with autoimmune pancreatitis. Antibodies against the plasminogen-binding protein (PBP) peptide were detected in 19 of 20 patients with autoimmune pancreatitis (95%) but also in 4 of 40 patients with pancreatic cancer (10%). Reactivity was not detected in patients with alcohol-induced chronic pancreatitis or intraductal papillary mucinous neoplasms. While the antibody was detected in most patients with autoimmune pancreatitis, it was also found in 10% of patients with pancreatic cancer making it an imperfect test to distinguish between these two conditions.

C. Imaging Studies

Table 28–3 summarizes the imaging findings observed in two large series, one from Massachusetts General Hospital (MGH) and the other from the Mayo Clinic. Pancreatic abnormalities were present in the majority of the patients and included diffuse enlargement, focal enlargement, and a distinct enlargement at the head of the pancreas. Noteworthy was the lack of vascular encasement calcification or pancreatic fluid; however, enlarged pancreatic lymph nodes were noted (Figures 28–1 and 28–2).