A 26-year-old woman comes to the office due to fatigue and poor sleep. For the past month, she has felt unusually tired and has been unable to keep up with her usual aerobics classes. Prior to the onset of symptoms, the patient began taking over-the-counter "energy" pills to improve stamina and promote weight loss. She wants to lose weight because she is getting married in a few months. Medical history is unremarkable; family history is also insignificant. The patient does not use tobacco, alcohol, or illicit drugs. Blood pressure is 138/66 mm Hg and pulse is 101/min. A resting hand tremor is noted. Ocular examination is normal. The thyroid gland is not palpable and there is no neck tenderness. The remainder of the physical examination is unremarkable. Thyroid function tests show TSH of <0.01 μU/mL and free T4 of 2.3 ng/dL (normal: 0.9-1.7) . Which of the following is most likely to be found on further evaluation of this patient?

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Explanation: 11ec2b69_c137_4d55_8f63_89caf5480367_MD0005_00 This patient has hyperthyroidism with tachycardia, tremor, and elevated free T4. She has no goiter or extrathyroidal manifestations (eg, proptosis) of Graves disease and no palpable nodules to suggest toxic nodular disease. In light of the association between the over-the-counter "energy" pills and the onset of symptoms, it is likely this patient has exogenous thyrotoxicosis due to desiccated thyroid extracts. Bovine and porcine thyroid supplements can be obtained without a prescription and have been promoted for weight loss and increased energy. Exogenous thyrotoxicosis can also be caused by excessive or surreptitious dosing of prescription thyroid medication. In the evaluation of exogenous thyrotoxicosis, 2 tests are helpful: The 24-hour radioactive iodine uptake (RAIU) is low with exogenous thyrotoxicosis as thyroid extracts suppress thyroid follicular activity. Other causes of hyperthyroidism with a low RAIU include inflammatory thyroiditis and, rarely, ectopic thyroxine production (eg, struma ovarii). If RAIU is low, thyroglobulin levels should be checked. With exogenous thyrotoxicosis, the concentration of thyroglobulin (released in small amounts by normal thyroid follicles) is also low due to suppressed follicular activity. Elevated serum thyroglobulin levels can be seen in patients with increased follicular activity (eg, Graves disease) or follicular injury (eg, thyroiditis). (Choice A) Elevated RAIU and thyroglobulin are seen in Graves disease. (Choice B) Low RAIU and elevated thyroglobulin are seen in various types of thyroiditis, such as postpartum thyroiditis and subacute granulomatous (ie, de Quervain) thyroiditis. (Choice C) Some patients with chronic lymphocytic (Hashimoto) thyroiditis can have transient thyrotoxicosis at the onset of disease. RAIU is variable and may be normal, and thyroglobulin is elevated due to inflammation of thyroid follicles. (Choice D) Toxic nodular disease typically shows elevated RAIU with a focal uptake pattern (as opposed to the diffuse pattern in Graves disease), although a normal RAIU may be seen. Thyroglobulin may also be low or normal as increased release from the toxic nodules is offset by decreased release from the remainder of the gland. However, this patient has no apparent nodules, and the temporal association with taking the over-the-counter supplement suggests exogenous thyrotoxicosis. Educational objective: Exogenous thyrotoxicosis can result from the intake of over-the-counter thyroid supplements or an excessive dosing of prescription thyroid medication. The activity of the thyroid gland is suppressed, with decreased radioactive iodine uptake and serum thyroglobulin levels. References: Factitious thyrotoxicosis and herbal dietary supplement for weight reduction. (http://www.ncbi.nlm.nih.gov/pubmed/18363120)

A 26-Year-Old Woman Comes to the Office Due to Fatigue