Thyroid-associated ophthalmopathy in black South Africans with Graves' disease: relationship to serum antibodies reactive against eye muscle and orbital connective tissue autoantigens.

Abstract

The prevalence of hyperthyroidism owing to Graves' disease is increasing among urban black South Africans. Thyroid-associated ophthalmopathy is often observed in this context, but its pathogenesis remains unclear. No close relationship has been noted between antiflavoprotein (Fp) antibodies or thyrotropin receptor antibodies and ocular involvement in black patients. We measured serum antibodies against eye muscle and orbital connective tissue antigens in black patients with Graves' disease, correlating them with eye signs. Of 11 patients with clinical ophthalmopathy, 2 (18%) had antibodies against collagen type XIII, 3 (27%) against flavine adenine dinucleotide (FAD), 1 (9%) against Fp, and 4 (35%) against G2s. Antibody prevalences in eight patients without clinical ophthalmopathy were 12.5% for collagen XIII, 12.5% for FAD, 25% for Fp and 0% for G2s. These differences were not statistically significant. None of the individual mean antibody levels were significantly different between the two subgroups of thyrotoxic patients. Serum antibody levels were negative in 10 black South African controls. In summary, eye muscle and orbital connective tissue antibodies were found in small proportions of patients with Graves' disease with no close relationship of any antibody to eye signs. Thus, a substantial proportion of black South Africans with overt clinical ophthalmopathy remains in whom currently availabe serologic tests are unhelpful for screening and laboratory confirmation.