Comparison Between Thyroid Stimulating Immunoglobulin and TSH-Receptor Antibodies in the Management of Graves' Orbitopathy.

Objectives: TSH-receptor antibodies (TRAb) targeting the TSH receptor (TSH-R) induce hyperthyroidism in Graves´ disease (GD). Graves´ orbitopathy (GO) is influenced by 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 the management of GO.

Methods: Patients with newly diagnosed GD (n=30, median age 55 years (range 35-72), 29 women) received pharmacological therapy (methimazole+++thyroxine) for 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 on five occasions during the 24-month follow-up. Twenty-two subjects completed the drug regimen without surgery or radioiodine treatment.

Results: At baseline, TSI was highly correlated with TRAb (r _s =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 for visit v1 (n=30, 17 GO during the whole study) or 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 the prediction and management of GO.