endocrine and metabolic disorders
Euthyroid Sick Syndrome
Introduction
Euthyroid sick syndrome is a condition in which serum levels of thyroid hormones are low in patients who have nonthyroidal systemic illness but who are actually euthyroid. Diagnosis is based on excluding hypothyroidism. Treatment is directed toward the underlying illness; thyroid hormone replacement is not indicated. (See also Overview of Thyroid Function .) Patients with various acute or chronic nonthyroid disorders may have abnormal Laboratory Testing of Thyroid Function . Such disorders include fasting, starvation, Decreased triiodothyronine (T3) levels are most common. Patients with more severe or prolonged illness also have decreased thyroxine (T4) levels. Serum reverse T3 (rT3) is increased. Thyroid -stimulating hormone (TSH) levels may be normal or even low, and during the recovery phase of the syndrome may be slightly elevated. Patients are actually euthyroid, but depending upon the underlying acute or chronic condition, may have features that overlap with severe hypothyroidism such as hypothermia, hypoventilation, hypotension, lethargy, or coma. Pathogenesis is unknown but may include Decreased peripheral conversion of T4 to T3 Decreased clearance of rT3 generated from T4 Decreased binding of thyroid hormones to thyroxine-binding globulin (TBG) Proinflammatory cytokines (eg, tumor necrosis factor-alpha, interleukin-1) may be responsible for some changes. Interpretation of abnormal thyroid function test results in ill patients is complicated by the effects of various drugs, including the iodine-rich contrast agents andamiodarone, which impairs the peripheral conversion of T4 to T3, and by drugs such asdopamineand corticosteroids, which decrease pituitary secretion of TSH, resulting in low serum TSH levels and subsequent decreased T4 secretion. Thyroid function tests should not be ordered for severely ill patients unless thyroid dysfunction is highly suspected. 