A 52-year-old woman comes to the office due to fatigue for the last 2 weeks. The patient was previously healthy, but over the past 3 months, she has had significant weight loss without changing her diet. She also reports increased sweating, hand tremor, and decreased sleep. Examination shows diffuse, nontender enlargement of the thyroid gland. The eyeballs are protuberant. The remainder of the examination is notable for 1+ pitting edema in the ankles. Which of the following parameters is most likely to be decreased in this patient?

Question

A 52-year-old woman comes to the office due to fatigue for the last 2 weeks.  The patient was previously healthy, but over the past 3 months, she has had significant weight loss without changing her diet.  She also reports increased sweating, hand tremor, and decreased sleep.  Examination shows diffuse, nontender enlargement of the thyroid gland.  The eyeballs are protuberant.  The remainder of the examination is notable for 1+ pitting edema in the ankles.  Which of the following parameters is most likely to be decreased in this patient?

Quizplus · Accepted Answer

11ec160b_3a8d_4235_9249_55583a77111f_MD0001_00 This patient with an enlarged thyroid gland and multiple consistent symptoms (eg, fatigue, unintentional weight loss, sweating, tremor, insomnia) most likely has hyperthyroidism. Protuberance of the eyeballs (ie, exophthalmos) suggests Graves disease, specifically. In adults, the major effect of thyroid hormone is control of cellular metabolism, including the rate of oxygen consumption and use of proteins, carbohydrates, and lipids. As a result, hyperthyroidism causes characteristic cardiovascular effects: Increased metabolic demand in the peripheral tissues, combined with a direct effect of thyroid hormone on vascular smooth muscle, causes peripheral vasodilation, which leads to decreased systemic vascular resistance (SVR) and reduced diastolic blood pressure. Thyroid hormone has a direct sympathetic-like effect on the myocardium, which stimulates increased heart rate and contractility (Choice A). A reflexive response to decreased SVR also contributes to these changes. With increased contractility, stroke volume is increased, resulting in increased pulse pressure and systolic blood pressure (Choices D and F). Ejection fraction and cardiac output are also increased. Over time, some patients develop high-output heart failure due to the hyperdynamic circulatory state. Restoration of a euthyroid state normalizes cardiovascular hemodynamics and typically resolves any heart failure that has developed. (Choice B) Myocardial oxygen consumption increases in hyperthyroidism, caused by a direct effect of thyroid hormone and by hemodynamic changes that increase myocardial oxygen demand (ie, increased heart rate, contractility, and afterload [systolic blood pressure]). (Choice C) Both diastolic and systolic pulmonary artery pressures increase in hyperthyroidism. This is likely because cardiac output increases, but the pulmonary circulation does not undergo the same vasodilation and reduction in resistance that occurs in the systemic circulation (pressure = cardiac output × resistance). Educational objective: Hyperthyroidism causes characteristic cardiovascular changes. Increased metabolic demand in the tissues and a direct vasodilatory effect of thyroid hormone lead to reduced systemic vascular resistance (and decreased diastolic blood pressure). A direct sympathetic-like effect of thyroid hormone on the myocardium leads to increased heart rate, contractility, and cardiac output. Increased stroke volume increases pulse pressure and systolic blood pressure.

A 52-Year-Old Woman Comes to the Office Due to Fatigue