A 25-year-old man comes to the office with a 2-month history of fatigue, palpitations, sweating, and heat intolerance. The symptoms are becoming more distressing and are keeping the patient awake at night. The patient has no diplopia, eye pain or redness, decreased vision, neck pain, or proximal muscle weakness. Medical history is unremarkable, and he currently takes no medications. He smoked for approximately a year during college but quit after graduation. The patient drinks alcohol socially but does not use recreational drugs. Family history is positive for hypothyroidism in his mother. Temperature is 36.7 C (98 F), blood pressure is 130/70 mm Hg, pulse is 115/min (regular), and respirations are 18/min. Examination shows an anxious, thin man in no acute distress. There is mild lid lag but no conjunctival erythema or proptosis. Extraocular movements and pupillary reflexes are intact. Mild diffuse nontender enlargement of the thyroid gland is noted. The skin is warm and moist. Cardiac examination is unremarkable except for tachycardia. Neurologic examination shows a fine hand tremor and brisk symmetrical reflexes but is otherwise unremarkable. Laboratory tests show normal complete blood count, basic metabolic profile, and urinalysis. Thyroid function test results are as follows: Radioactive iodine uptake at 24 hours is 36% (normal: 8%-25%), and scan shows a diffuse uptake pattern. Serum thyroid-stimulating immunoglobulin level is mildly elevated. Treatment options are explained to the patient. Six weeks later, he returns to the office and says that his symptoms have resolved. Blood pressure is 120/80 mm Hg and pulse is 82/min. Eye examination reveals no lid lag. The thyroid examination is unchanged, and the rest of the examination is unremarkable. Which of the following tests is most likely to be helpful in this patient?

Question

A 25-year-old man comes to the office with a 2-month history of fatigue, palpitations, sweating, and heat intolerance.  The symptoms are becoming more distressing and are keeping the patient awake at night.  The patient has no diplopia, eye pain or redness, decreased vision, neck pain, or proximal muscle weakness.  Medical history is unremarkable, and he currently takes no medications.  He smoked for approximately a year during college but quit after graduation.  The patient drinks alcohol socially but does not use recreational drugs.  Family history is positive for hypothyroidism in his mother.  Temperature is 36.7 C (98 F), blood pressure is 130/70 mm Hg, pulse is 115/min (regular), and respirations are 18/min.  Examination shows an anxious, thin man in no acute distress.  There is mild lid lag but no conjunctival erythema or proptosis.  Extraocular movements and pupillary reflexes are intact.  Mild diffuse nontender enlargement of the thyroid gland is noted.  The skin is warm and moist.  Cardiac examination is unremarkable except for tachycardia.  Neurologic examination shows a fine hand tremor and brisk symmetrical reflexes but is otherwise unremarkable.  Laboratory tests show normal complete blood count, basic metabolic profile, and urinalysis.  Thyroid function test results are as follows:  Radioactive iodine uptake at 24 hours is 36% (normal: 8%-25%), and scan shows a diffuse uptake pattern.  Serum thyroid-stimulating immunoglobulin level is mildly elevated. Treatment options are explained to the patient.  Six weeks later, he returns to the office and says that his symptoms have resolved.  Blood pressure is 120/80 mm Hg and pulse is 82/min.  Eye examination reveals no lid lag.  The thyroid examination is unchanged, and the rest of the examination is unremarkable.  Which of the following tests is most likely to be helpful in this patient?

Quizplus · Accepted Answer

Explanation: Laboratory evaluation to assess thyroid function is typically performed 4-6 weeks after initiation of antithyroid drug (ATD) treatment and then every 2-3 months. TSH may remain suppressed for several months after initiation of therapy and does not accurately reflect thyroid functional status (Choice E). For this reason, total T3 and free T4 levels should be used to assess efficacy of ATD therapy, especially early in the treatment course. This patient has symptomatically improved; if his total T3 and free T4 levels are normalized he can proceed to definitive therapy. (Choices A and B) The major life-threatening side effects of ATDs are agranulocytosis and hepatotoxicity. Agranulocytosis usually occurs within 90 days of initiation and presents with fever, chills, or sore throat. If patients on ATDs develop these symptoms, a white blood cell count with differential should be obtained; if agranulocytosis is confirmed, the ATD should be stopped immediately. Blood counts are often ordered at baseline but do not need to be repeated in the absence of symptoms. Hepatotoxicity is a potential adverse effect of propylthiouracil but is rare with methimazole. As with blood counts, hepatic markers are typically ordered at baseline but do not need to be repeated in the absence of symptoms (eg, pruritus, jaundice, loss of appetite). (Choice C) Autoantibodies to the TSH receptor may assist in the initial diagnosis of Graves disease. They are also used to predict relapse in patients who have been treated with an ATD; persistent titers correlate with an increased risk of relapse. However, TSH receptor antibodies do not reflect thyroid functional status or response to treatment. Educational objective: Serum total T3 and free T4 levels are used to assess thyroid function during treatment with antithyroid drugs. TSH may remain suppressed for several months following initiation of therapy and does not reliably reflect thyroid functional status. 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/21700562)

A 25-Year-Old Man Comes to the Office with a 2-Month