Tachycardia in a 61-Year-Old Woman

Jeffrey Siegelman, MD; Daniel M. Lindberg, MD

Disclosures

June 24, 2015

Discussion

This patient's ECG showed atrial fibrillation with a rapid ventricular response, which is a possible cardiac manifestation of thyrotoxicosis (Figure). No ischemic changes were noted despite her rapid heart rate.

The patient's laboratory studies confirmed the suspected diagnosis; she had a markedly depressed thyroid-stimulating hormone (TSH) level of 0.006 mIU/L (normal range, 0.5-5.0 mIU/L) and elevated triiodothyronine (T3) and thyroxine (T4) concentrations of 632 ng/dL (normal range, 70-170 ng/dL) and 23.7 µg/dL (normal range, 5-11 µg/dL), respectively.

"Thyrotoxicosis" refers to an elevated concentration of thyroid hormone as well as its related clinical manifestations. This is differentiated from thyroid storm, a life-threatening manifestation of thyrotoxicosis in which a markedly hypermetabolic state is present.

Hyperthyroidism most commonly results from uncontrolled Graves disease, in which autoantibodies to the TSH receptor are produced. This leads to excessive thyroid hormone production from the thyroid gland and a reflexive inhibition of TSH release from the pituitary gland. Other etiologies can include a solitary thyroid adenoma, toxic multinodular goiter, hypersecretory thyroid carcinoma, thyrotropin-secreting pituitary adenoma, struma ovarii, and iodine or amiodarone administration.

A precipitating event, such as surgery, trauma, myocardial infarction, pulmonary embolism, diabetic ketoacidosis, childbirth, severe infection, discontinuation of antithyroid medication, or thyroid surgery in a patient with uncontrolled hyperthyroidism, is often needed to push a patient with hyperthyroidism into thyroid storm.[1,2]

The incidence of hyperthyroidism in the United States is 0.05%-1.3%, most of which remains undiagnosed. Approximately 1%-2% of these patients progress to thyroid storm at some point. The prevalence is slightly higher in women than men, and in white and Hispanic populations than in black populations. Thyroid storm is most common in the third to sixth decades of life, although it can occur at any age.[1]

Thyroid storm is a clinical diagnosis and, considering the acuity of this life-threatening condition, patients with thyrotoxicosis should be treated empirically when the diagnosis is suspected. Symptoms of thyrotoxicosis include weight loss, palpitations, hair loss, diplopia, chest pain, oligomenorrhea, or confusion. The physical examination reveals a hypermetabolic state, with abnormalities involving multiple organ systems. These findings commonly include hyperpyrexia, tachycardia, tachypnea, and hypertension. Other findings may include fine tremor, exophthalmos, ophthalmoplegia, pretibial edema, congestive heart failure, thyromegaly, thyroid bruit, and hyperreflexia.[3]

Laboratory studies show a low TSH level and elevated T3 and T4 concentrations. TSH is the most precise indicator of thyroid function because of the very high sensitivity of the thyroid/pituitary feedback loop, and current assays are able to detect levels ≤ 0.02 mIU/L. As such, a normal TSH level largely excludes significant thyroid disease. Other laboratory findings seen in thyrotoxicosis may include hyperglycemia, hypercalcemia, leukocytosis, and elevated liver enzymes.[2]

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