Does IgG4 level at the time of diagnosis correlate with disease outcome in IgG4-Related disease?

BACKGROUND/OBJECTIVES: Serum IgG4 level is used as a diagnostic criterion for immunoglobulin G4-related disease (IgG4-RD) but whether it predicts disease progression is unclear. Aim of the study was to investigate if serum IgG4 level at the time of diagnosis correlates with disease outcome. METHODS: Patients with a definitive diagnosis of IgG4-RD were included in this study. They were divided into two groups - Group 1: Elevated serum IgG4 at diagnosis and Group 2: Normal serum IgG4 at diagnosis. Outcome parameters including multiple organ involvement, exocrine and endocrine dysfunction, relapse and mortality were compared. Data was subanalysed for outcomes on 2 levels of serum IgG4 cut-off - A: The upper limit of normal (ULN) and B: Twice the ULN. RESULTS: Of 47 patients, 31 (66%) patients had elevated serum IgG4 at diagnosis. There was no statistically significant difference between the two groups in any of the outcome parameters. Data analysed with the serum IgG4 levels > ULN showed no difference between the 2 groups for any of the outcome parameters. However, when the serum IgG4 cut-off was set to twice the ULN, there was a significantly higher rate of disease relapse (42.9% vs 11.5%, p = 0.02) and pancreatic exocrine insufficiency (PEI) (76.2% vs 42.3%, p = 0.041). CONCLUSION: Raised serum IgG4 greater than two times the ULN was significantly associated with disease relapse and PEI in patients with IgG4-RD. Larger multicentre studies with longer follow-up are required to corroborate these findings and define the role and cut-off value of serum IgG4 in outcomes of IgG4-RD.