A 36-year-old woman comes to the office due to a 6-month history of lethargy and poor sleep. She has non-restorative sleep with frequent awakening throughout the night. The patient has also had a loss of appetite and decreased interest in day-to-day activities. In addition, she has had irregular menses, with infrequent, heavy, painless menstrual bleeding. There is no associated weight change, fever, cough, dyspnea, palpitations, abdominal pain, constipation, cold intolerance, or dry skin. Past medical history is unremarkable, and the patient takes no medications. She has a 10-pack-year smoking history, drinks alcohol socially, and does not use recreational drugs. Family history is positive for Graves disease in a sister and hypertension in her father. On examination, her blood pressure is 136/90 mm Hg, pulse is 78/min, and BMI is 27 kg/m². The thyroid gland is diffusely enlarged and firm on palpation. Cardiopulmonary examination is normal, with no pedal edema. No focal neurological deficits are noted. Laboratory results show TSH of 9 μU/mL (normal 0.35-4.5 μU/mL), free T4 of 1.2 ng/dL (normal 0.8-1.8 ng/dL), and anti-thyroid peroxidase antibody present in high titers. Repeat TSH level is 8.8 μU/mL. Which of the following is the best next step in this patient's care?

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Explanation: 11ec2b69_becf_0009_8f63_cbb601ad9b11_MD0005_00 This patient has subclinical hypothyroidism associated with irregular menses and symptoms suggestive of depression. Subclinical hypothyroidism is a state of mild thyroid dysfunction characterized by an elevated TSH level in the presence of a normal free thyroxine (T4) level. Subclinical hypothyroidism is often asymptomatic, but it can be associated with a variety of somatic and cognitive symptoms. Patients with subclinical hypothyroidism and a TSH >10 μU/mL or elevated titers of antithyroid peroxidase antibodies have a high likelihood of progression to overt hypothyroidism and are likely to benefit from levothyroxine replacement therapy. Patients with a TSH of 4.5-10 µU/mL and typical symptoms of hypothyroidism or diffuse goiter may also benefit from treatment. In addition, women with ovulatory dysfunction/infertility or who are pregnant or planning to get pregnant should be offered levothyroxine. This patient has a diffuse goiter, symptoms suggestive of depression, and ovulatory dysfunction, along with a positive antithyroid peroxidase antibody titer suggesting early chronic lymphocytic (Hashimoto) thyroiditis. She should therefore be started on levothyroxine therapy. (Choice A) This patient should receive levothyroxine therapy. Patients who have subclinical hypothyroidism with TSH <10μU/mL and any of the additional risk factors described above can be monitored (eg, repeat thyroid function tests every 6-12 months). (Choice B) Conversion of T4 to T3 is regulated by TSH. Patients with primary hypothyroidism can have normal circulating T3 levels despite impaired thyroid function because of increased peripheral conversion due to elevated TSH levels. Serum T3 measurement is therefore of limited utility in hypothyroidism. (Choice C) Both overt and subclinical forms of depression associated with hypothyroidism may improve with treatment of hypothyroidism alone. (Choice D) T3 is the active form of thyroid hormone and is produced primarily by conversion from T4 in peripheral tissues. However, T3 has a very short half-life, and treatment with liothyronine (oral T3 supplement) produces wide fluctuations in blood levels. Therefore, liothyronine supplementation is not recommended for routine use. Educational objective: Subclinical hypothyroidism is characterized by a normal free thyroxine (T4) level with an elevated TSH. Indications for levothyroxine therapy in subclinical hypothyroidism include hypothyroid symptoms, pregnancy, infertility or ovulatory dysfunction, goiter, positive antithyroid antibody titers, and TSH >10 μU/mL. References: Subclinical hypothyroidism: an update for primary care physicians. (http://www.ncbi.nlm.nih.gov/pubmed/19121255)

A 36-Year-Old Woman Comes to the Office Due to a 6-Month