Association of clinical course with thyroid-stimulating immunoglobulin in Graves' ophthalmopathy in Mongolians

Graves' ophthalmopathy (GO) is a complex inflammatory condition affecting the orbit and is often associated with Graves' disease (GD). This study aims to determine the levels of thyroid-stimulating immunoglobulin (TSI) and thyroid-stimulating hormone receptor autoantibody (TSHR-ab) in the serum of patients with GO, compare it with the GD, and determine whether there is a correlation with the clinical course of GO. The cross-sectional study included 82 patients with GO, 81 patients with GD, and 75 healthy subjects. The ocular manifestations of GO were identified and evaluated by the clinical activity score (CAS) and severity of GO using the European Group of Graves' Orbitopathy (EUGOGO). TSI and TSHR-ab levels in the serum of participants were determined with ELISA kits and correlated with clinical findings. A total of 238 participant's data were analyzed. There were 14 patients (17%) with unilateral GO. The most common ocular signs were eyelid retraction 68 (82.3%) and proptosis 61 (74.4%). The mean CAS score was 2.65 +/- 1.64 in GO patients and was higher in men than women (P = 0.008). The mean of TSI was 37.95 +/- 35.41 in GO, 14.16 +/- 15.67 in GD, and 4.33 +/- 2.94 in healthy controls (P<0.0001). The TSI was significantly higher in patients with GO than in those with GD (P<0.0001). There were no correlations between TSI and TSHR-ab levels and CAS scores. However, we observed a correlation between the TSI level and the severity of GO (P = 0.023). The area under the ROC curve (AUC) of TSI was 0.933 and selected 14.1 IU/ml was the optimal cutoff value (98.78% of sensitivity, 83.97% of specificity). Our study showed that TSI is significantly related to GO and the severity of GO. Therefore, TSI can be used as a predictor of severe GO to help in prognostication, follow-up and treatment planning.