Association of thyrotrophin receptor antibodies with the clinical features of Graves' ophthalmopathy

Abstract

Objective: Graves' ophthalmopathy (GO) and Graves' hyperthyroidism are closely associated diseases and thought to be caused by the same autoimmune process. An obvious explanation for this would be the presence of autoantibodies reacting with an autoantigen present in the orbit and the thyroid gland. The TSH-Receptor (TSH-R) antibodies are a likely candidate, because they cause Graves' hyperthyroidism and the TSH-R appears to be present also in orbital tissues. If TSH-R antibodies are responsible for the ophthalmopathy one would expect their titres to correlate with clinical characteristics of the eye disease. The aim of the present study is to see whether TSH-R antibodies are related to the activity and severity of the thyroid-associated ophthalmopathy.

Design and patients: TSH-R antibody levels were measured as TBII (TRAK assay), and TSI (cAMP response of a TSH-R transfected cell line) in serum of 63 patients with untreated moderately severe GO, accompanying Graves' thyroid disease; all patients had been euthyroid for > 2 months.

Results: TBII and TSI titres were strongly related to each other. TBII or TSI titres did not correlate with thyroidal or orbital disease duration, nor with TPO antibody levels. In contrast, we found a striking and highly significant correlation between the Clinical Activity Score (CAS) of the eye disease, and both TBII (r = 0.54; P < 0.0001) and TSI (r = 0.50; P < 0.0001). In addition, a weaker but significant relation was found between proptosis (in mm) and TBII (r = 0.36; P = 0.004) and TSI (r = 0.49; P = 0.0001). No correlation was found with eye muscle motility.

Conclusion: TSH-R antibody levels correlate directly with clinical features of Graves' ophthalmopathy. The results support the hypothesis of a pathogenetic role of TSH-R antibodies and the TSH-R in the orbit of Graves' ophthalmopathy patients.