MKSAP Quiz: Follow-up evaluation for hyperthyroidism

Answer and critique

The correct answer is D. Radioactive iodine (¹³¹I) therapy. This item is Question 61 in MKSAP 18's Endocrinology and Metabolism section.

The most appropriate management is radioactive iodine (¹³¹I) therapy. The patient's examination findings and thyroid scintigraphy results are consistent with a diagnosis of toxic adenoma. Toxic adenoma and multinodular goiter are the second most common cause of hyperthyroidism overall and are most frequently seen in older adults. These autonomously functioning nodules synthesize and secrete thyroid hormones independent of thyroid-stimulating hormone (TSH) stimulation as a result of activating mutations of the TSH receptor or G_sα. They are usually large and can be easily palpated on examination. First-line treatment options include radioactive iodine therapy or surgery. Radioactive iodine is the most commonly used first-line treatment. The radioisotope ¹³¹I emits both gamma and beta radiation. Gamma radiation can be detected by the camera to determine radioactive iodine uptake and create an image of the thyroid gland during thyroid scintigraphy, whereas beta radiation yields the therapeutic effect by triggering thyroid follicular cell death. If a patient has a particularly large goiter with compressive symptoms or if there is concern for malignancy, surgery is recommended as first-line therapy.

Autonomous nodules are associated with a very low risk of malignancy (<1%), and fine-needle aspiration biopsy is not indicated. If biopsy is performed, it frequently yields indeterminate cytology results, such as suspicion for follicular neoplasm, and generates inappropriate concern and unnecessary recommendations for follow-up examinations and biopsies.

Increasing the atenolol dosage and prescribing methimazole are also not the best management options. While β-blockers ameliorate adrenergic symptoms, they do not address the underlying cause. This patient has a normal heart rate and blood pressure on her current dose of atenolol, so increasing this further is not indicated.

Antithyroid drugs (methimazole) are not first line for managing hyperthyroidism because spontaneous remission does not occur and treatment would have to be continued indefinitely.