A 26-year-old woman comes to the physician to monitor her thyroid medication. She has a history of papillary thyroid cancer that was treated with a subtotal thyroidectomy and ablative radioiodine 3 years ago. The tumor was 2.1 cm in greatest dimension without lymph node involvement or distant metastasis. She currently takes 125 mcg of levothyroxine on an empty stomach every morning and has no current symptoms. Laboratory tests show undetectable thyroglobulin, undetectable anti-thyroglobulin antibodies, TSH of 4.8 μU/mL, and free T₄ of 1.3 ng/dL (normal 0.8-1.8 ng/dL). One year ago, her total body radioactive iodine scan and neck ultrasound were unremarkable. Which of the following is the most appropriate next step in management of this patient?

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Explanation: 11ec2b69_bed9_6060_8f63_afa10ca032c0_MD0005_00 After treatment of thyroid cancer with surgery and ablative radioiodine therapy, patients frequently require thyroid replacement therapy due to loss of healthy thyroid tissue. In addition, high TSH levels stimulate the growth of residual thyroid cancer cells, and suppressing TSH with levothyroxine has been shown to decrease the risk of recurrent disease. However, suppressive doses of levothyroxine are associated with an increased risk of bone loss and atrial fibrillation. Therefore, the degree of TSH suppression will depend on the initial tumor stage and risk of recurrence. If the risk of recurrence is low, such as in this patient, levothyroxine supplementation should be provided to suppress TSH just below the normal range for the initial 6-12 months following thyroidectomy and radioactive iodine therapy. Then, if the patient is free of recurrence, the TSH levels should subsequently be maintained in the lower half of the normal range (Choice C). In patients with large, aggressive tumors, or distant metastasis, the TSH is typically kept below 0.1 µU/mL for several years after initial treatment (Choice E). (Choice A) Liothyronine (T₃) supplementation is not warranted for chronic treatment of hypothyroidism. T₃ can be used in place of levothyroxine for a short period to prevent symptoms of hypothyroidism in patients with thyroid cancer who are holding levothyroxine in preparation for radioactive iodine uptake and scan. (Choice B). Levothyroxine should be taken on an empty stomach, separately from other medications. Taking levothyroxine with meals or other medication can impair its absorption and make management erratic or unpredictable. Educational objective: TSH suppression with levothyroxine has been shown to decrease the risk of recurrence of differentiated epithelial thyroid cancers. The degree of TSH suppression depends on the initial stage of the cancer and risk of recurrence. References: Revised American Thyroid Association management guidelines for patients with thyroid nodules and differentiated thyroid cancer. (http://www.ncbi.nlm.nih.gov/pubmed/19860577)

A 26-Year-Old Woman Comes to the Physician to Monitor Her