A 24-year-old female maintained on methimazole for the treatment of Graves disease comes to your office after having a positive urine pregnancy test. She complains of mild nausea, but does not have any other symptoms. Her last menstrual period was five weeks ago. She was diagnosed with Graves disease approximately eight months ago. Her clinical symptoms of hyperthyroidism have markedly improved since starting methimazole. She is married and has no children. She does not smoke or drink alcohol. Her mother has hypothyroidism. She takes no other medications. She has no medication allergies. Her menstrual cycles were previously regular. Physical examination reveals a mildly enlarged, smooth, non-tender thyroid gland. Thyroid function tests performed last week showed a TSH of 0.7 mU/L and total T₄ of 15.2 μg/dL (normal 4 to 12 μg/dL). What is the best next step in this patient's management?

Question

Quizplus · Accepted Answer

Explanation: This patient's hyperthyroidism has been relatively well maintained on her dose of methimazole. Her current TSH is just below the normal range. While her total T₄ is elevated, it is expected to be higher than normal during pregnancy because of increased thyroid binding globulin synthesis. Thionamide medications are the treatment of choice for hyperthyroidism in pregnancy since both radioiodine and surgery should be avoided. However, methimazole is a potential teratogen and should not be used during the first trimester. These teratogenic effects consist of scalp defects, tracheoesophageal fistula, and choanal atresia. During the first trimester, pregnant patients should be switched to propylthiouracil, which carries less risk of birth defects. For the second and third trimesters, patients are often switched back to methimazole because propylthiouracil carries a risk of liver failure. (Choice A) Beta-blockers can be given if a pregnant patient has symptoms of hyperthyroidism despite the use of thionamide medications, although an attempt should be made to avoid beta-blockers since they can potentially result in harmful effects on the fetus. The most important step at this time is to switch methimazole to propylthiouracil in order to avoid its teratogenic effects. (Choice C) Methimazole can be used in the second and third trimesters of pregnancy, but should be avoided during the first trimester because of its teratogenic effects. (Choice D) Surgery can be considered for pregnant patients with severe symptoms despite thionamide use, but in general an attempt should be made to avoid surgery during pregnancy. (Choice E) Radioiodine therapy is absolutely contraindicated during pregnancy because it can ablate the fetal thyroid gland. Educational objective: Thionamides are the treatment of choice for hyperthyroidism during pregnancy. Propylthiouracil should be used in the first trimester because of concerns of teratogenic effects with methimazole. Patients should be switched to methimazole for the second and third trimesters because of potential liver failure in patients taking propylthiouracil.

A 24-Year-Old Female Maintained on Methimazole for the Treatment of Graves