Q1 : A 9-year-old girl presents with a 2-month history of diarrhea and weight loss. A thorough review of systems reveals that she has been having difficulty sleeping at night for the past month. On physical examination, her heart rate is 95 beats/min, blood pressure is 121/85 mm Hg, weight is 22 kg, and height is 132 cm. You palpate a firm enlarged thyroid gland without nodules. Laboratory studies reveal a free thyroxine (FT4) value of 2.4 ng/dL (30.9 pmol/L) (normal, 0.9 to 1.6 ng/dL [11.6 to 20.6 pmol/L]) and
thyroid-stimulating hormone (TSH) value of less than 0.01 mIU/L (normal, 0.5 to 4.0 mIU/L). Of the following, the next BEST step in the management of this patient is to
A. assess thyroid-stimulating immunoglobulins
B. perform I-123 uptake scan
C. repeat FT4 and TSH measurements in 1 week
D. start methimazole
E. start propylthiouracil
The Answer :
The girl described in the vignette has classic signs and symptoms of Graves disease (autoimmune hyperthyroidism).
Given her degree of tachycardia, hypertension, and laboratory evidence of hyperthyroidism, she should be treated with antithyroid medications immediately.
Methimazole is the clear antithyroid medication of choice because the risk of potentially fatal liver toxicity with propylthiouracil
(PTU) has been well documented in recent years.
PTU should not be used in the management of Graves
disease unless there is a strong contraindication to other medical or surgical therapy. Both methimazole and PTU inhibit thyroid hormone biosynthesis by decreasing the oxidation of iodide and iodination of tyrosine.
Although PTU offers the additional theoretical advantage of diminishing peripheral conversion of thyroxine into triiodothyronine, the risk of liver dysfunction outweighs the potential benefit.
Methimazole should be administered at a dose of 0.5 to 1 mg/kg per day divided twice a day and can be given in conjunction with a long-acting beta-blocker to alleviate symptoms until the FT4 value is normal. For patients who cannot tolerate antithyroid medication, alternate options for treating Graves disease include thyroidectomy or I-131 ablation.
Measurement of thyroid-stimulating immunoglobulins for the girl in the vignette would not be helpful in the management of her disease.
When additional evidence is needed to confirm the diagnosis
(ie, results of physical examination and laboratory tests are not classic), assessment of antibodies or I- 123 scanning may be helpful.
If hashitoxicosis (short-term hyperthyroidism sometimes seen in acute destruction of thyroid tissue due to Hashimoto thyroiditis) is suspected, the presence of thyroid peroxidase antibodies and absence of thyroid-stimulating immunoglobulins can help make the correct diagnosis.
An I-123 uptake scan could be helpful in differentiating between hashitoxicosis (patchy uptake), exogenous thyroid intake (low uptake), or Graves disease (high uptake).
Additional tests, including a repeat measurement of her FT4 and TSH 1 week later, are not indicated.
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