Elevation of serum IgG4 in Western patients with autoimmune sclerosing pancreatocholangitis: a word of caution.

Background: Autoimmune pancreatocholangitis is characterized by sclerosing inflammation of the biliary tree or pancreatic duct and can mimic pancreaticobiliary malignancy. Serum immunoglobin (Ig) G4 values seem to be helpful in distinguishing autoimmune pancreatocholangitis from pancreatic malignancy in the Japanese population; however, its significance in the Western population has not been well studied.
Methods: We report a retrospective analysis of 7 consecutive patients with autoimmune pancreatocholangitis and compare them to 23 patients with pancreatic malignancy. Clinical presentation, diagnostic tests, and preoperative IgG4 levels were reviewed in all patients. Presence of autoimmune pancreatocholangitis or pancreatic malignancy was determined by pathologic analysis in all patients and reviewed by a single pathologist.
Results: In all patients, autoimmune pancreatocholangitis manifested in a similar fashion to pancreatic malignancy. Median IgG4 levels were far lower in pancreatic cancer patients with localized, resectable disease (24 mg/dL), locally advanced disease (24 mg/dL), and metastatic disease (28 mg/dL) as compared with patients with autoimmune pancreatocholangitis (142 mg/dL, P < .05). Only one patient with pancreatic cancer had an IgG4 level that was >100 mg/dL. In contrast, all patients with autoimmune pancreatitis or cholangitis had levels >100 mg/dL. However, in five of these seven patients, IgG4 levels were below the upper limits of normal.
Conclusions: Autoimmune pancreatocholangitis mimics pancreatobiliary malignancy. Serum IgG4 values seem to be helpful in distinguishing autoimmune pancreatocholangitis from malignancy in the Western population. However, absolute values seem to be lower in the United States compared with Japan. The upper limit of normal as reported in laboratories in the United States may not be useful in identifying abnormally high IgG4 values. A new upper limit of normal may need to be defined because IgG subclass determinations are being used more frequently in Western patients with biliary obstruction.