Serology in autoimmune pancreatitis

Autoimmune pancreatitis (AIP) is the pancreatic manifestation of a systemic immune-driven, inflammatory process that can involve organs such as the bile duct, salivary glands and lymph nodes, in addition to the pancreas. Many of the presenting signs and symptoms of AIP, including painless jaundice, weight loss and mild epigastric pain, are characteristic of pancreatic adenocarcinoma; thus, obtaining an accurate diagnosis to avoid unnecessary surgery is imperative. AIP responds very well to steroid treatment, although it may recur in up to 20% to 40% of cases. The diagnostic criteria for AIP are histological, radiographic, clinical and laboratory-based in nature. Although no international consensus on diagnostic criteria has yet been made, some of the diagnostic features of AIP include elevated gamma globulin, immunoglobulin, and, in particular, immunoglobulin G4 fraction (IgG4). The search for a distinct serological marker of AIP has included antibodies to a wide range of antigenic stimuli. To date, there have been studies of AIP and antibodies to lactoferrin, carbonic anhydrase isoforms II and IV, pancreatic secretory trypsin inhibitor (PSTI or SPINK) as well as to less sensitive or specific markers of autoimmunity, such as antinuclear antibody and rheumatoid factor. Although there are some preliminary strengths of association with PSTI antibodies, none of these biomarkers appears to be sensitive or specific enough to serve as distinctive evidence of AIP. At the current time, elevations of IgG4 to greater than 280 mg/dL remain the most reliable and reproducible indicator that a patient has AIP.