Significance of serum antibodies reactive with flavoprotein subunit of succinate dehydrogenase in thyroid associated orbitopathy

Aims-Thyroid associated orbitopathy (TAO) is an autoimmune disorder of extraocular muscles and orbital connective tissue. Identification of the principal target antigens would help the understanding of the pathogenesis of the disease and possibly lead to the development of specific therapies in the future. The purpose of this study was to measure serum antibodies against the flavoprotein subunit of succinate dehydrogenase in patients with TAO and correlate their presence with factors of TAO. Methods-Sera of patients with active TAO of 6 months' duration or less were tested for antibodies against the flavoprotein subunit of succinate dehydrogenase. Clinical data were obtained by retrospective review of patients' charts. Enzyme Linked immunosorbent assay was used to test sera for serum antibodies against purified succinate dehydrogenase. Results-38 patients with TAO and 32 healthy age and sex matched controls were included in the study. Anti-flavoprotein antibodies were detected in 24 out of 38 patients with TAO (63.16%) and in five out of 32 healthy controls (15.63%) (p<0.01). Neither age, sex, duration of thyroid disease, thyroid status, treatment of thyroid disease, smoking history, duration of orbitopathy, activity of orbitopathy, nor the presence of lid retraction were significantly associated with the presence of serum antiflavoprotein antibodies (p>0.05). However, the total number of rectus muscles affected in both eyes of the patients was significantly correlated with the finding of a positive antibody test (p<0.05). Conclusions-Serum antibodies reactive with the flavoprotein subunit of succinate dehydrogenase are associated with extraocular muscle involvement in active TAO of recent onset.