A 31-year-old woman comes to the office with a 3-month history of palpitations and weight loss. She weighs 110 kg (243 lb); 3 months ago, she weighed 118 kg (260 lb). There is no associated dysphagia, neck pain, or hoarseness, and her menstrual periods have been regular. The patient was previously healthy and her family history is unremarkable. She does not use tobacco or alcohol. The patient is sexually active with one partner and uses a barrier method for contraception. Temperature is 36.7 C (98.1 F), blood pressure is 140/90 mm Hg, pulse is 102/min, and respirations are 20/min. The thyroid gland cannot be clearly felt on examination due to body habitus. Ocular examination is unremarkable. Laboratory tests show an elevated serum free triiodothyronine and thyroxine and low TSH. A urine pregnancy test is negative. Radioactive iodine scan reveals uptake of tracer only in the right thyroid lobe, as shown in the image below. Which of the following processes is responsible for this patient's elevated thyroid hormone levels?

Question

A 31-year-old woman comes to the office with a 3-month history of palpitations and weight loss.  She weighs 110 kg (243 lb); 3 months ago, she weighed 118 kg (260 lb).  There is no associated dysphagia, neck pain, or hoarseness, and her menstrual periods have been regular.  The patient was previously healthy and her family history is unremarkable.  She does not use tobacco or alcohol.  The patient is sexually active with one partner and uses a barrier method for contraception.  Temperature is 36.7 C (98.1 F), blood pressure is 140/90 mm Hg, pulse is 102/min, and respirations are 20/min.  The thyroid gland cannot be clearly felt on examination due to body habitus.  Ocular examination is unremarkable.  Laboratory tests show an elevated serum free triiodothyronine and thyroxine and low TSH.  A urine pregnancy test is negative.  Radioactive iodine scan reveals uptake of tracer only in the right thyroid lobe, as shown in the image below.  Which of the following processes is responsible for this patient's elevated thyroid hormone levels?

Quizplus · Accepted Answer

11ec25c8_d0be_6c49_bc81_1d5ac879db7b_MD0003_00 This patient has clinical thyrotoxicosis (eg, palpitations, tachycardia, weight loss) with elevated thyroid hormone levels and a suppressed TSH, consistent with primary hyperthyroidism. The radioactive iodine scan reveals unicentric uptake only in the right lobe, thereby confirming the diagnosis of toxic adenoma. Both toxic adenoma and multinodular goiter have a nodular pattern of uptake; however, in contrast to the focal uptake of radioactive iodine in toxic adenoma, uptake in patients with multinodular goiter shows a patchy distribution. Normally, TSH is the major driver for the production of thyroid hormones. However, the hyperplastic cells in toxic adenoma and toxic multinodular goiter overproduce thyroid hormone autonomously without TSH stimulation. Some of these patients have activating somatic mutations of the TSH receptors on the hyperplastic follicular cells, leading to TSH-independent activation of adenylyl cyclase. (Choice A) Hyperthyroidism in Graves disease results from thyroid-stimulating autoantibody-induced activation of TSH receptors on thyroid follicular cells. Radioiodine uptake is diffuse rather than focal, and patients usually have additional extrathyroidal manifestations (eg, exophthalmos, pretibial myxedema). (Choice C) Surreptitious intake of thyroid hormone is occasionally seen in patients who are attempting to lose weight. In such cases, radioiodine uptake is diffusely reduced. (Choice D) TSH is elevated or inappropriately normal in hyperthyroidism resulting from TSH-secreting pituitary tumors. (Choice E) Release of preformed thyroid hormone is seen in various forms of thyroiditis, including subacute (de Quervain) thyroiditis, silent thyroiditis, and the transient hyperthyroid phase seen in some patients with chronic lymphocytic (Hashimoto) thyroiditis. Radioactive iodine uptake in these cases is markedly reduced. Educational objective: Hyperthyroidism from toxic adenoma is due to autonomous production of thyroid hormones from the hyperplastic thyroid follicular cells. The radioactive iodine uptake scan reveals uptake only in the hyperactive nodule, with suppression of uptake in the rest of the gland.

A 31-Year-Old Woman Comes to the Office with a 3-Month