Review Question - QID 221273

This patient with anxiety, weight loss, heat sensitivity, and amenorrhea as well as decreased TSH and elevated free T4 most likely has hyperthyroidism. The single thyroid nodule with increased iodine uptake is consistent with a thyroid adenoma.

Toxic adenomas are benign thyroid tumors resulting from hyperplasia of thyroid follicular cells, producing increased amounts of triiodothyronine (T3) and thyroxine (T4). They most often occur in younger patients and are slow-growing. Patients will present with signs of hyperthyroidism including anxiety, palpitations, heat intolerance, weight loss, and oligomenorrhea in women. On exam, a single palpable nodule will often be present. Laboratory studies will show decreased TSH and increased T3 and T4. To distinguish a toxic adenoma from other causes of hyperthyroidism, an RAIU is often done. A toxic adenoma will reveal localized uptake of radioactive iodine, with sparing throughout the rest of the thyroid gland. Patients with overt hyperthyroidism due to toxic adenomas require treatment. This includes symptomatic relief with beta-blockers, radioiodine ablation, surgery, or suppressive thioamide therapy.

Shim et al. studied cancer risk after radioactive iodine treatment for hyperthyroidism. The authors found that there was no evidence of increased cancer risk after exposure to radioiodine (RAI) in general; however, there was a dose-dependent increased risk for thyroid cancer. The authors recommend that primary care clinicians pay attention to the RAI dosages received by their hyperthyroid patients.

Figure/Illustration A is a radioactive iodine uptake (RAIU) test of the thyroid gland showing focal uptake of radioactive tracer (red circle). This finding is suggestive of a toxic thyroid adenoma.

Incorrect Answers:
Answer 1: Grave disease is the most common cause of hyperthyroidism. It is an autoimmune disorder resulting from TSH receptor antibodies that overstimulate thyroid hormone synthesis and release. Patients will often present with a diffusely enlarged thyroid gland, extrathyroidal manifestations such as pretibial myxedema and exophthalmos, and diffusely increased radioactive iodine uptake on RAIU.

Answer 2: Hashimoto thyroiditis is a chronic autoimmune thyroiditis that results in a painless goiter. Although it can rarely manifest as hyperthyroidism, Hashimoto thyroiditis is the most common cause of hypothyroidism in non-iodine-deficient areas.

Answer 3: Struma ovarii is a rare cause of hyperthyroidism that occurs when an ovarian tumor produces ectopic thyroid tissue. It usually occurs in women between 40 and 60 years of age and presents with a pelvic mass and abdominal pain. The thyroid gland will not be enlarged, and RAIU will reveal reduced thyroid uptake.

Answer 4: Subacute thyroiditis, also known as de Quervain thyroiditis, is a self-limited inflammatory disease of the thyroid gland that can cause transient hyperthyroidism. The patient will have a tender goiter and RAIU will show decreased radioiodine uptake.

Bullet Summary:
A toxic adenoma is a benign tumor that will present with hyperthyroidism, a nontender palpable nodule, and focal uptake on radioactive iodine uptake studies.