A 49-year-old woman comes to the clinic due to night sweats, palpitations, and heat intolerance for the last 4 weeks. She used to exercise regularly to stay "in good shape," but her energy level has been too low for exercise over the last 2 weeks. The patient has no past medical problems and takes no medications, including over-the-counter drugs. Her mother underwent a thyroidectomy 15 years ago.
Blood pressure is 140/70 mm Hg and pulse is 104/min. BMI is 22 kg/m². The patient has mild lid lag but no proptosis. She has fine tremors involving her hands. Thyroid examination reveals a palpable nodule in the left thyroid lobe. The remainder of the examination is unremarkable.
Her TSH is <0.01 µU/mL. T₃ and free T₄ are elevated. Urine pregnancy test is negative.
Which of the following tests will be most helpful in identifying the cause of this patient's current condition?

Question

Quizplus · Accepted Answer

11ec193a_97b3_9937_853d_89de795f5d2b_MD0002_00 This patient's presentation is consistent with thyrotoxicosis. Graves' disease (GD) is the most common cause of hyperthyroidism, and the diagnosis can often be made clinically when extrathyroidal manifestations (ie, ophthalmopathy) and a diffuse nontender goiter are present. However, this patient has no specific features of GD and has a palpable nodule suggesting a toxic nodule (TN). For patients with hyperthyroidism who do not have obvious features of GD, radioactive iodine uptake (RAIU) is recommended in the initial evaluation. Normal or elevated RAIU indicates de novo thyroid hormone synthesis; decreased or absent uptake indicates thyroid destruction (thyroiditis) with release of preformed hormone. Patients with nodular findings should have thyroid scan in conjunction with RAIU. The pattern of radioiodine uptake on a thyroid scan differentiates between GD (diffuse uptake), toxic multinodular goiter (patchy areas of increased and decreased uptake), and TN (increased uptake in the nodule and decreased uptake in the remainder of the thyroid) in patients with normal or elevated RAIU. (Choice A) Erythrocyte sedimentation rate is elevated in subacute thyroiditis (de Quervain's thyroiditis), which usually has associated thyroid pain and tenderness. However, this patient's lack of tenderness makes the diagnosis less likely. (Choice C) Serum thyroglobulin is checked in suspected surreptitious thyroid hormone use, and the level is characteristically low in these patients. The thyroid gland is usually small or non-palpable in surreptitious thyrotoxicosis, and this patient's palpable nodule suggests TN. (Choice D) Thyroid ultrasound has limited utility in the evaluation of hyperthyroidism. It is recommended to evaluate non-toxic nodules to assess for malignant characteristics, but toxic nodules are rarely malignant. If RAIU and thyroid scan identify a hyperfunctioning nodule, ultrasound is not needed. (Choice E) Thyrotropin receptor antibodies may be useful if GD is strongly suspected clinically but the extrathyroidal manifestations are not present. Antibody tests using recombinant thyrotropin receptor have a very high sensitivity and specificity for GD. Educational objective: Radioactive iodine uptake can differentiate between increased synthesis of thyroid hormone and release of preformed hormone in patients with hyperthyroidism. A concurrent thyroid scan is recommended to identify a toxic nodule or toxic multinodular goiter in hyperthyroid patients with palpable nodules. __________ References: Hyperthyroidism and other causes of thyrotoxicosis: management guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists. (http://www.ncbi.nlm.nih.gov/pubmed/21510801)

A 49-Year-Old Woman Comes to the Clinic Due to Night