Elevated Immunoglobulin G4 Levels in Patients with Thyroid Eye Disease and Their Clinical Implications

PURPOSE. The purpose of this study was to assess the relationship between thyroid eye disease (TED) in patients undergoing orbital decompression and immunoglobulin G4 (IgG4) levels. METHODS. A prospective observational cohort study was conducted among 185 consecutive patients who were diagnosed with TED and underwent orbital decompression. Serum levels of IgG4 were measured, and immunohistochemical staining for IgG and IgG4 was performed in orbital adipose tissue. Data related to clinicopathologic features were analyzed. RESULTS. Among the 185 enrolled patients with TED, 64 (34.6%) were IgG4-positive. The IgG4-positive patients were older, had higher clinical activity scores (CAS), and had worse best-corrected visual acuity (BCVA) than the IgG4-negative patients. Higher thyrotropin receptor antibody (TRAb) levels, histopathological IgG4 counts, IgG4/IgG ratios, and dense lymphocyte infiltration were more frequently observed in IgG4-positive than in IgG4-negative patients. Definitive and probable IgG4 subtypes were independently associated with the active stage in patients with TED. CONCLUSIONS. Our data suggest that the IgG4 subtype in TED is common. IgG4-positive patients with TED may be older, have more severe disease, and have higher clinical activity scores. IgG4 may play an important role in the pathogenesis of TED.