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Thread: A 42-year-old female visits ED with Palpitations & SOB - USMLE Sample # 144

  1. #1

    A 42-year-old female visits ED with Palpitations & SOB - USMLE Sample # 144

    A 42-year old female visits the emergency department with complaints of palpitations and shortness of breath. An EKG shows sinus tachycardia at 124 bpm and chect xray shows cardiomegaly. Past history reveals insomnia. Blood investigations reveal a low TSH but the free T4 is increased. The patient is started on intravenous propranolol. Propranolol is likely to benefit this patient by decreasing which of the following?

    A. Peripheral conversion of T4 to T3
    B. Release of T4 by the thyroid gland
    C. New thyroid hormone synthesis
    D. Tissue oxygen consumption
    F. Serum levels of TSH receptor antibodies
    Thanks & Regards
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  2. #2
    Most likely option A. Peripheral conversion of T4 to T3

  3. #3
    The Peripheral conversion of T4 to T3 is the correct answer

  4. #4
    Correct Answer: A. Peripheral conversion of T4 to T3

    Explanation:

    This patient shows symptoms and signs of mild congestive heart failure and signs of a hypermetabolic, hyper adrenergic state and thyrotoxicosis. The mechanism of action of receptor blockers in thyrotoxicosis is through a decrease in the effect of sympathetic adrenergic impulses reaching target organs and a decrease in the rate of peripheral conversion of T4 to T3.

    (Choice B) β-receptor blockers (i.e. beta blockers) are not known to affect thyroid hormone release. In thyrotoxicosis, such release can be reduced by administration of pharmacologic doses of iodine.

    (Choice C) Beta blockers are not known to after thyroid hormone synthesis. Propylthiouracil or methimazole are administered to decrease the synthesis of thyroid hormone.

    (Choice D) In thyrotoxicosis and other hyperthyroid states, beta blockers improve some manifestations of excessive thyroid hormone action, but not all. Hyperthyroid symptoms/signs that are not improved by β blockers include: increased tissue oxygen consumption, circulating thyroxine levels, weight loss, and—in the case of Grave’s disease— exophthalmos.

    (Choice E) Beta blockers do not affect serum levels of TSH receptor antibodies.

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