Ultrasound in hyperthyroidism

I saw a 32-year-old man in consultation for hyperthyroidism. His thyroid-stimulating hormone was <0.01 and both free T₄ and free T₃ were elevated. He had palpitations, tremor and insomnia but denied other symptoms. On exam, his thyroid was non-tender and without nodules. More than likely his diagnosis is Graves’ disease, I thought.

After discussing the treatment options in detail, we both leaned towards methimazole (Tamazole, King). At first, I did not think that radioactive iodine uptake and scan would be needed as we were not planning on radioactive iodine therapy.

I performed thyroid ultrasound as I do for most of my hyperthyroid patients. Incidental thyroid nodules are uncommon in Graves’ disease; however, if a thyroid nodule is present, it could change our management recommendations. If such a nodule was biopsied and confirmed to be cancer, then the treatment for both the malignancy and the hyperthyroidism would be surgery.

This patient had a homogenous thyroid without nodules (Figure 1). However, I noticed something that did not quite fit with a diagnosis of Graves’ disease: There was almost no flow in his intrathyroidal arteries. Usually the blood flow of a Graves’ disease thyroid is markedly increased (Figure 2). This is sometimes called “thyroid inferno.”

Figure 1.

Figure 2.

Source: Thomas B. Repas, DO, FACP, FACE, CDE

I changed my mind about not ordering radioactive iodine imaging. The radioiodine uptake was <1%, consistent with hyperthyroidism due to painless thyroiditis. As expected, both thyroid stimulating immunoglobulins and thyrotropin receptor antibodies were negative.

Instead of treating with antithyroid medication as I might have had if he had Graves’ disease, we will follow his thyroid function over the next several weeks. I expect he will develop transient hypothyroidism in the near future. Hopefully, he will be one of the patients whose thyroid function eventually returns to normal.

I suspect that if my patient had an ultrasound performed by a technician instead of myself, the unexpected lack of blood flow would have been overlooked. There is a chance that I might even have misdiagnosed him with Graves’ disease and initiated unnecessary therapy.

Ultrasound is not often used to determine the cause of hyperthyroidism. In some situations, however, thyroid ultrasound can be useful in clarifying the diagnosis. This includes pregnancy, when radioactive iodine imaging is not an option, as well as in determining whether a patient has type 1 vs. type 2 amiodarone-induced thyrotoxicosis. Some thyroidologists may find ultrasound occasionally helpful in other causes of hyperthyroidism as well.