Diagnosis of Thyroid Eye Disease
If your doctor suspects that you have an overactive or underactive thyroid gland, your thyroid function must first be evaluated and treated appropriately by an internist trained in doing so. Treatments include medications to suppress the production of hormone by the thyroid gland, radioactive iodine to eliminate hormone-producing cells, or surgery to remove the thyroid tissue. In most cases, replacement thyroid hormone is required following the natural course of the Graves’ autoimmune attack on the thyroid gland or following effective treatment. Once your thyroid function is treated and returned to normal, the eye disease must be monitored as it often continues to progress. Eye involvement must be evaluated on a continuing basis by an ophthalmologist during the active phase of the disease and, if necessary, treated. Although symptoms often resolve on their own, disease activity, scarring, and visual loss not readily apparent to the patient may otherwise go unnoticed and cause permanent changes.
There is good evidence to suggest that radioactive iodine treatment poses significant risks to worsening thyroid eye disease. The presence of significant eye disease is a relative contraindication to radioactive iodine treatment. Even with mild or no eye disease, treatment with oral steroids at the time of radioactive iodine treatment is usually indicated, to reduce the risks to the eye.
Following thyroid ablation, with radioactive iodine or thyroidectomy surgery, it is critically important to treat the resultant hypothyroid state rapidly. Following surgery, this means initiating treatment within a week of total thyroidectomy. Following radioactive iodine treatment, this usually means rechecking thyroid levels at 6 weeks post treatment and reassessing frequently (every 4-8 weeks) until thyroid hormone levels stabilize with treatment.
There is also conflicting evidence on the role of prolonged methimazole use in the development of thyroid eye disease. Methimazole does not treat the underlying problem, which is the auto-immune disease directed against thyroid gland antigens. Methimazole only treats the resultant hyperthyroid endocrine state. European studies suggest that prolonged methimazole treatment does not increase the risk of thyroid eye disease, but the studies were limited to patients with no underlying eye disease. American studies suggest that in the presence of some eye disease, prolonged methimazole treatment is a significant risk factor for worsening disease. This is also our anecdotal experience at the University of Michigan. We typically recommend endocrine stabilization with methimazole followed by definitive treatment with either radioactive iodine or thyroidectomy surgery, depending on the rest of the clinical picture (including severity of the eye disease).