I’d really like to go on my bike ride

A 46-year-old woman had a history of hyperthyroidism due to Graves’ disease. After two years of methimazole, she was weaned off therapy and was euthyroid for almost 10 years. In Oct. 2009, her thyroid-stimulating hormone was 0.89 mIU/L and free thyroxine (T₄) 0.83 ng/dL (0.8 ng/dL–1.8 ng/dL).

Then in April 2010, she experienced sudden onset of palpitations, tremor and insomnia. Radioactive iodine uptake was markedly increased, confirming recurrent Graves' disease. TSH was <0.01 mIU/L, free-T4 1.08 ng/dL and free triiodothyronine (T₃) 4.11 pg/mL (2.0 pg/mL – 3.5 pg/mL) .

She was reinitiated by her primary care physician on methimazole 10 mg three-times daily. Repeat TSH on June 3 was still suppressed (<0.01 mIU/L). She had been prescribed propranolol, but did not take it because it caused fatigue and exercise intolerance. Her greatest concern is whether she would be able to participate in a several day bicycle ride in New England — this month.

She came to see me to find out her options. As a fellow athlete, I can relate. It is frustrating to train for an important event and then be sidelined because of illness. Many physicians might have told her, “Why don’t you think about staying home?”

However, I didn’t think that was the best advice, unless there were truly no other options.

Our question is what should we do now? There certainly are no expert guidelines about how to prepare someone with hyperthyroidism to safely participate in a several day bicycle ride.

Although she was willing to proceed with radioactive iodine therapy, radioiodine would not be expected to take effect for at least 2 to 4 months. Thus, even though radioiodine is an option we will need to discuss in the future, it will not solve the issue of how to prepare her for her bicycle ride. Thus, the best option would be to achieve euthyroidism, if possible.

Agents such as glucocorticoids and bile acid sequestrants have been reported to be helpful in more rapidly controlling hyperthyroidism when used in combination with antithyroid medication, but I have had only limited success with them. Oral iodine, such as saturated solution of potassium iodide (SSKI), would rapidly control thyrotoxicosis. Typically we reserve SSKI for thyroid storm or prior to surgery. If necessary, I might have been willing to consider. However, because iodine can interfere with radioiodine therapy and some patients experience relapse several weeks later it was not my first choice.

Not sure of how to proceed, I ordered additional laboratory studies. Despite her TSH being fully suppressed, her free T₄ is now 0.83 ng/dL and her free T3 is 2.09 pg/ml. I reassured her there is often a lag time between levels of thyroid hormone and TSH. She should not to worry about the continued TSH suppression. I was optimistic she was responding and would be able to go on her ride.

Repeat labs last week found her TSH 0.89 mIU/L and free T₄ 0.96 ng/dL. Not wanting to induce iatrogenic hypothyroidism, I decided to decrease her methimazole to once-daily. We will recheck TSH, free T₄ and free T₃ one last time — the Monday before she leaves for her ride.

As a precaution we agreed that wearing a heart rate monitor would be a good idea. I also advised her that instead of pushing the pace as she normally might, it would be wise to hang back with the slower riders. As I said, there are no expert guidelines regarding how to approach situations such as this. It would have been easy to say, “You’re hyperthyroid and shouldn’t go”, but it would not have been best for this patient. It is essential for physicians to be willing to individualize therapy to meet the needs and unique circumstances of their patients.