Endocrine Abstracts

Immunoglobulin G4-related disease (IgG4-RD) is a newly identified syndrome characterized by high serum IgG4 levels and increased IgG4-positive plasma cells infiltration. IgG4-related thyroiditis (IgG4-RT) was first prescribed based on the immunohistochemistry in 2009. Some of Hashimoto’s thyroiditis (HT), Graves’ disease (GD) and Riedel thyroiditis were reported to be classified as IgG4-RT based on high serum IgG4 level or histopathological findings. However, the prevalence of IgG4-RT in HT and GD varies in previous reports. There were inconsistent results in the clinical features in IgG4-RT and its relationship to thyroid auto-antibodies. This study is to evaluate serum IgG4 levels in subjects with autoimmune thyroid disease (ATD), and the relationship of serum IgG4 level and thyroid auto-antibodies. A total 185 subjects, including 23 men and 162 women with thyroid diseases were enrolled. 58 subjects had GD in remission, 61 subjects had HT, and 66 subjects had goiter or multinodular as control group. All participants did not receive any anti-thyroid drugs, levothyroxine, or immunosuppressive treatment. The median (interquartile range) serum IgG4 levels were 51.4 (34.4–105.0), 53.4 (32.5–86.8), and 67.5 (38.3–111.0) mg/dl in subjects with GD, HT, and goiter, respectively. There was no significant differences of serum IgG4, IgG levels, and IgG4/IgG ratio between these three groups. There were 9 (15.8%), 5 (8.2%), and 14 (21.2%) subjects had elevated IgG4 levels (>135 mg/dl) defined by serological diagnostic criteria of IgG4-RD in each group, which also showed no statistical differences. Of these 28 subjects with elevated IgG4 levels, 6 (21.4%) were male, which showed a higher male proportion. The mean age was 45.3±12.4 years, which was younger than those with normal IgG4 levels (50.8±11.4 years). However, there were no significant differences in thyroid auto-antibodies, including TSH receptor (4.3±8.7% vs 6.4±10.1%, P=0.313), anti-TPO (122.6±198.7 IU/ml vs 229.6±457.0 IU/ml, P=0.225), and anti-thyroglobulin (119.9±264.7 IU/ml vs 217.6±870.5 IU/ml, P=0.558) antibodies between subjects with elevated IgG4 and without elevated IgG4. Only one subjects was diagnosed of monoclonal gammopathy of undetermined significance. There was no significant extra-thyroid organ involvement as seen in IgG4-RD in the other 27 subjects. There were no significant differences in serum IgG4 levels, and the prevalence of elevated serum IgG4 level in subjects with GD, HT, and goiter in this study.