Antibodies against striated muscle, connective tissue and nuclear antigens in patients with thyroid-associated ophthalmopathy: should Graves' disease be considered a collagen disorder?

Abstract

The identity and subcellular localization of the principal extraocular muscle (EOM) antigens and prevalences of the corresponding serum autoantibodies in thyroid-associated ophthalmopathy (TAO) need to be clarified. We have used porcine eye muscle tissue, which expresses all autoantigens identified in human tissue, as substrate in an indirect immunofluorescence assay. Several different patterns of antibody binding to EOM tissue antigens were observed with sera from patients with TAO namely, membrane, cytoplasmic, interstitial (endomysial) and nuclear. Overall, sera from 75% of patients with TAO contained one or more antibodies reactive with EOM, compared to 32% of patients with Graves' hyperthyroidism, 38% with Hashimoto's thyroiditis, and 16% of normals. All sera which reacted with EOM membrane or cytoplasmic antigens also reacted with the same antigen(s) in other skeletal muscle, but not in the other tissues tested. Sera from 31% of patients with TAO, but only 7% of those with Hashimoto's thyroiditis, and no patient with Graves' hyperthyroidism without evident ophthalmopathy, contained antinuclear antibodies (ANA). The most common nuclear fluorescence pattern was the finely speckled type typically associated with anti-Sm or anti-RNP antibodies. Significant positive correlations in patients with TAO were found between (i) EOM dysfunction and ANA (ii) eye disease of < 1 yr duration and EOM membrane-reactive antibodies and (iii) eye disease of < 1 yr duration and interstitial (endomysial) tissue-reactive antibodies. Although patients with Graves' disease do not usually exhibit other signs or immunologic features of a generalized collagen disorder, the finding of high prevalences of ANA and anti-striated muscle antibodies and, less often, anti-connective tissue antibodies in patients with ophthalmopathy, is consistent with it being a collagen-like disorder of the striated muscle, connective tissue and the thyroid. The reason why the inflammatory process is mainly limited to these tissues is unclear although cross reaction of ANA with tissue specific proteins or increased expression of muscle and connective tissue antigens in the orbit and skin, are possibilities.