A 70-year-old-man is admitted to the hospital with acute retrosternal chest pain and severe shortness of breath. His other medical conditions include hypertension and hyperlipidemia. Coronary angiography reveals critical stenosis of the left main coronary artery, and the patient subsequently undergoes emergency coronary artery bypass grafting. On the fourth postoperative day, he develops atrial flutter with a rapid ventricular response. Thyroid function test results are as follows:
| Free thyroxine (free T4) | 1.4 ng/dL (normal: 0.9-2.4 ng/dL) |
| Triiodothyronine (T3), total | 70 ng/dL (normal: 115-190 ng/dL) |
| Thyroid-stimulating hormone (TSH) | 0.7 mU/L (normal: 0.5-5.0 mU/L) |
Which of the following is the most likely etiology of this patient's abnormal thyroid function tests?
Euthyroid sick syndrome (low T3 syndrome) | |
Risk factors |
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Pathophysiology |
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Diagnostic testing |
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Management |
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ICU = intensive care unit. | |
Thyroid function tests are often abnormal in patients with severe, acute illness. Severe illness is associated with decreased peripheral 5'-deiodination of T4 to T3 due to caloric deprivation, increased glucocorticoid and inflammatory cytokine release, and inhibitors of 5'-monodeiodinase (eg, free fatty acids). The most common pattern is low total and free T3 levels with normal T4 and TSH, often called euthyroid sick syndrome. However, many experts consider this a misnomer and believe it represents a mild transient central hypothyroid state that serves as an adaptive response to severe illness. If the underlying illness continues, T4 and TSH levels may eventually decrease.
In general, thyroid function testing in hospitalized patients should be avoided; however, it may be necessary in certain circumstances (eg, to rule out hyperthyroidism in acute atrial fibrillation). When a euthyroid sick syndrome pattern is found, thyroid hormone supplementation does not improve clinical outcomes and is not indicated. During recovery, patients may experience a modest, transient increase in TSH, which may be misinterpreted as subclinical hypothyroidism. Therefore, follow-up testing should be delayed until the patient has returned to baseline health.
(Choice A) Chronic lymphocytic (Hashimoto) thyroiditis is characterized by autoimmune destruction of thyroid follicles. It usually presents with chronic hypothyroidism (ie, low T4, high TSH), although a transient hyperthyroid phase (ie, high T4, low TSH) is sometimes seen. Normal TSH and T4 are not consistent with this disorder.
(Choice B) Drug-induced hypothyroidism is a common adverse effect of amiodarone, which is occasionally given for atrial fibrillation. However, this results in high TSH and low T4 levels, which are not seen in this patient.
(Choice D) Overt central hypothyroidism is characterized by a low T4 level with low (or inappropriately normal) TSH. This patient's T4 is normal.
(Choice E) Subclinical hypothyroidism is characterized by elevated TSH with normal T4 (and T3) levels. Although subclinical hyperthyroidism (ie, low TSH, normal T4) is associated with increased risk for atrial fibrillation, this patient has normal TSH.
Educational objective:
Thyroid function tests are often abnormal in patients with severe, acute illness. The most common pattern is low T3 with normal T4 and TSH (ie, euthyroid sick syndrome), which may represent an adaptive response to severe illness. Thyroid hormone supplementation is not indicated for these patients, and follow-up testing should be delayed until the patient has returned to baseline health.