Comparison between thyroid stimulating immunoglobulin and TSH-receptor antibodies in management of Graves' orbitopathy.

Introduction TSH-receptor antibodies (TRAb) targeting the TSH receptor (TSH-R) induce hyperthyroidism in Graves´ disease (GD). Graves´ orbitopathy (GO) is influenced by a stimulation of the TSH-R in the orbita. GO has been, among other factors, linked to high TRAb levels. Thyroid stimulating immunoglobulins (TSI) is a relatively new method for assessing TSH-receptor antibodies. The aim of this study was to investigate the role of TSI in management of GO. Materials and methods Patients with newly diagnosed GD (n=30, median age 55 years (range 35-72), 29 women) received pharmacological therapy (methimazole + thyroxine) up to 24 months. GO was identified by clinical signs and symptoms. Eleven patients had GO at diagnosis and another six developed GO during treatment. Blood samples for TSI and other thyroidal biomarkers were obtained at baseline and at five occasions during the 24-month follow-up. 22 subjects completed the drug regimen without surgery or radioiodine treatment. Results At baseline, TSI was highly correlated with TRAb (rs=0.64, p<0.001), and both assays similarly correlated to fT3 values. TSI and TRAb did not differ significantly between GO and non-GO patients neither for visit v1 (n=30, 17 GO during the whole study), nor at follow-up (n=22, 12 GO during the whole study). During follow-up, levels of TSI and TRAb decreased and normalized in both groups. Conclusion The present study does not support any added benefit of TSI compared to TRAb for prediction and management of GO.