A new diagnostic endoscopic tool for autoimmune pancreatitis.

Background: Autoimmune pancreatitis (AIP) is a type of pancreatitis that is presumed to have an autoimmune etiology, and is currently diagnosed based on a combination of clinical, laboratory, and imaging studies. Although it is of utmost importance that AIP be differentiated from pancreatic cancer, AIP is sometimes difficult to differentiate from locally advanced pancreatic cancer.

Objective: To find a useful new method to diagnose AIP.

Design: Prospective study from June 2004 to September 2007.

Setting: Single public hospital.

Patients: Ten AIP patients, 10 patients with pancreatic cancer, and 10 patients with papillitis.

Interventions: Immunoglobulin (Ig)G4-immunostaining of biopsy specimens obtained from the major duodenal papilla.

Main Outcome Measurements: Number of immunohistochemically identified cells per high-power field (HPF) in each specimen were counted.

Results: Significant infiltration of IgG4-positive plasma cells (> or = 10/HPF) was observed in the major duodenal papilla of all 8 AIP patients with pancreatic head involvement. Moderate infiltration of IgG4-positive plasma cells (4-9/HPF) was detected in 1 patient with pancreatic head cancer, but there were rare (< or = 3/HPF) IgG4-positive plasma cells infiltrating the major duodenal papilla in 2 AIP patients who only had pancreatic body and/or tail involvement, 9 patients with pancreatic cancer, and 10 patients with papillitis. In the 3 AIP patients in whom biopsy specimens were retaken after steroid therapy, the number of IgG4-positive plasma cells decreased from significant to moderate in 2 patients and to < or = 3/HPF in 1 patient.

Limitations: Small sample size. Endoscopists were not blinded to clinical information.

Conclusions: IgG4 immunostaining of biopsy specimens obtained from the major duodenal papilla may be useful for supporting a diagnosis of AIP with pancreatic head involvement.