An 80-year-old woman is admitted to the intensive care unit with sepsis due to a urinary tract infection. While in the ICU she develops atrial fibrillation with rapid ventricular response and is treated with a loading dose of amiodarone. She converts to sinus rhythm and is sent home on amiodarone to prevent recurrences of atrial fibrillation. In the following weeks she develops increasing fatigue, dry skin, and constipation and her internist finds her TSH to be 25. She is in sinus rhythm. What is the best approach in this situation?
Correct Answer: Start low dose levothyroxine and repeat TSH in 6 weeks.
Description: Amiodarone is a widely used antiarrhythmic drug. It is related structurally to thyroid hormone and is stored in adipose tissue. The drug has a high iodine content as well. Taking amiodarone on an ongoing basis can lead to hypothyroidism by inhibiting deiodinase activity and by acting as a direct antagonist to T4 . In some cases, amiodarone-induced hypothyroidism resolves within a few months; however, in many, especially when accompanying anti-TPO antibodies are present, treatment with levothyroxine is needed. This can be easily monitored and adjusted. While answer a is a consideration, the patient likely needs the amiodarone given her tendency toward paroxysms of atrial fibrillation and the attendant risk of stroke. While starting a beta-blocker may prevent episodes of rapid ventricular response, this decision would be made with the help of her cardiologist, which is not mentioned. Anti-TPO antibodies increase the risk of hypothyroidism but are not necessary to guide therapy in this patient. Although prednisone may be used for treatment of amiodarone-induced hyperthyroidism, this patient has hypothyroidism, and prednisone is not indicated.
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