Anti-eye Muscle IgG and IgM Antibodies are Associated with Eye Muscle Type 2 Deiodinase Activities in Hyperthyroid Graves’ Ophthalmopathy

Objective: Antibodies to eye muscle tissue are demonstrated in hyperthyroid Graves’ disease but their pathognomonic roles have not been clarified yet. We suggest that type 2 deiodinase (DIO2) enzyme can be a target between orbital and thyroid diseases in hyperthyroid Graves’ ophthalmopathy. In this study, the relationship between anti-eye muscle membrane (EyeM) and cytosol (EyeC) IgG, IgA and IgM antibodies and eye muscle DIO2 activity was investigated in hyperthyroid Graves’ disease. Methods: Thirty-two patients with hyperthyroid Graves’ disease (20 had ophthalmopathy), mean age 36 ± 13 years, 27 females and 5 males formed the patient group. Thyroid hormone levels were measured with chemiluminescence immunoassay, antithyroid antibody and anti-eye muscle antibody levels with enzyme-linked immunosorbent assay, but TSH receptor antibodies with radioimmunoassay. Eye muscle DIO2 activity was measured using I-T4. Results: EyeM and EyeC IgG antibodies were associated with increased eye muscle DIO2 activity compared to those who were negative for these antibodies (2.79 ± 2.53 vs 17.88 ± 20.06 pmol/mg/min, P<0.015 for EyeM-IgG and 6.88 ± 9.62 vs 26.76 ± 23.86 pmol/mg/min, P<0.008 for EyeC-IgG). The difference in EyeC-IgM antibodies was significant between patients with and without ophthalmopathy (10.1 ± 4.73 vs 3.46 ± 3.18 pmol/mg/min, P<0.023). The presence of EyeM-IgM antibodies was associated with lower eye muscle DIO2 activities with significantly decreased eye muscle thicknesses (8.51 ± 15.38 vs 2.6 ± 0.1 pmol/mg/min and 4.71 ± 1.23 vs 3.9 ± 0.14 mm, P<0.04). Conclusion: Anti-eye muscle antibodies were associated with increased or decreased eye muscle DIO2 activities affecting eye muscle thicknesses in hyperthyroid Graves’ ophthalmopathy. DIO2 enzyme can be a new target between orbital and thyroid diseases in hyperthyroid Graves’ ophthalmopathy.