Radio active iodine treatment:-Radio active iodine(I-131) is widely used to treat the thyrotoxicosis of graves’ disease, but, despite its demonstrable efficacy and safety profile, there have long been concerns about its possible adverse effect on thyroid eye disease. Definitive evidence for this link has been presented in a large ,well designed study by Bartalena etal19 treated 443 patients with Graves’ disease and mild or no ophthalmopathy with methimazole until euthyroid ,then randomly allocated them to continued methimazole, radioiodine, or radioiodine with adjuvant corticosteroid therapy.The results of the study were clear cut. After radioiodine treatment 15% of patients developed new or worsened ophthalmopathy. It confirms the results of a previously done randomized trial, which was criticized on methodological ground.20 Two plausible theories have been elucidated1.The first is that radiation induced thyroid damage releases some kind of antigens resulting in immune mediated ophthalmopathy, second is that rapid hypothyroid state due to radio iodine stimulates the release of TSH causing retro orbital adipocyte proliferation.
Type of thyroid disease -TED is associated with 90 % patients with hyperthyroidism,7% with euthyroid , 3% with hashimotos thyroiditis and 1% with primary hypothyroidism.1,4 Even if the patient is euthyroid, thyroid associated orbitopathy may progress. Other related autoimmune disorders like myasthenia gravis, which is about 50 times more common in patients with TAO in comparison to normal population, signify worsen the prognosis. 21,22 Similarly, patients having TAO and diabetes mellitus seem to have a higher incidence of dysthyroid optic neuropathy (DON).23,24
Studies for the assessment of various risk factors of TAO found in literature are summarized here. In a longitudinal cohort study done by Stein JD et al25, all patients 18 years of age or older with newly diagnosed Grave’s disease who were continuously enrolled in a large nationwide US managed care network and who visited an ophthalmologist 1 or more times from 2001 to 2009 were identified. Multivariable Cox regression was used to determine the hazard of developing TAO among persons with newly diagnosed GD, with adjustment for social and demographic parameters, systemic co morbidities, , and medical and surgical interventions for management of hyperthyroidism. In follow up of 8404 patients with GD who met the inclusion criteria, 740 (8.8%) developed TAO. Surgical thyroidectomy, alone or in combination with medical therapy, was associated with a 74% decreased hazard for TAO (adjusted HR, 0.26 95% CI, 0.12-0.51) compared with radioactive iodine therapy alone. Statin use (for ?60 days in the past year vs <60 days or nonuse) was found to be associated with a 40% decreased hazard.