Serum immunoglobulin G4 associated with number and distribution of extrapancreatic lesions in type 1 autoimmune pancreatitis patients

Background and Aim: Type 1 autoimmune pancreatitis (AIP) is characterized by the increase of serum immunoglobulin (Ig)G4 and abundant IgG4 plasma cell infiltration in the pancreas and various extrapancreatic lesions (EPL), which are proposed as IgG4-related disease. We assessed the correlation between serum IgG4 and the number of EPL, and the association between serum IgG4 and the distribution of EPL in type 1 AIP patients. Methods: Serum IgG4 was measured in 35 type 1 AIP patients and 71 non-AIP patients. The clinical characteristics and distribution of eight EPL were determined in 35 type 1 AIP patients. Results: Serum IgG4 in type 1 AIP was significantly higher than in non-AIP (P < 0.001). A total of 33 patients had EPL among 35 patients with type 1 AIP (94.3%). There was a significant correlation between serum IgG4 and the number of EPL (rho = 0.75, P < 0.001). Further, to assess the association between serum IgG4 and the distribution of EPL, type 1 AIP patients were divided into two groups: as abdominal localized EPL and systemic EPL. Both serum IgG4 and total numbers of EPL in systemic EPL were remarkably higher than those in abdominal localized EPL. Serum IgG4 cut-off value was 346 mg/dL to distinguish between abdominal localized EPL and systemic EPL according to the receiver-operator characteristic curve data. Conclusions: Our findings indicated that serum IgG4 was useful in both the diagnosis of type 1 AIP and the detection of systemic EPL. Our finding may help the concept and diagnostic criteria of IgG4-related disease with type 1 AIP.