Performing a radioactive iodine (¹²³I) uptake and scan is the most appropriate management for this patient, who most likely has a toxic nodule or nodules as the cause for her mild hyperthyroidism. Since multiple nodules were identified on ultrasound, it is important to ascertain which of the nodules are autonomous, as the likelihood of malignancy in such lesions is very low. Performing a thyroid scan will help identify whether one or more of the nodules is responsible for her thyroid function abnormalities.

A thyroid scan will also determine if fine-needle aspiration is indicated elsewhere in the gland. Nodules identified as autonomously functioning (or “hot”) do not require fine-needle aspiration, whereas nodules that are either “cold” or “warm” (of similar uptake to the surrounding non-nodular thyroid tissue) may require cytologic evaluation.

This patient may ultimately benefit from methimazole therapy, but since her hyperthyroidism is mild, it is safe to wait to initiate medical therapy until after the thyroid scan is performed. In patients with a greater degree of thyrotoxicosis, beginning methimazole to lower the thyroid hormone levels prior to performing additional testing is reasonable. Once the hormone levels are nearing the normal range, the thionamide should be withheld for 5 days prior to the thyroid scan.

If the patient is found to have a toxic nodule or multiple toxic nodules, surgical removal is a reasonable treatment approach, particularly if there are compressive symptoms from the goiter. Since this is considered an elective procedure, administering low-dose methimazole to normalize of her thyroid hormone levels would be advisable prior to surgery.