EUTHYROID SICK SYNDROME

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. few Patients with various acute or chronic nonthyroid disorders may also have abnormal thyroid function test results. Such disorders include fasting, starvation, protein-energy undernutrition, severe trauma, myocardial infarction, chronic kidney disease, diabetic ketoacidosis, anorexia nervosa, cirrhosis, thermal injury, drug overdose, and sepsis. Decreased triiodothyronine (T3) levels are most common. Patients with more severe or prolonged illness also have decreased thyroxine (T4) levels. 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 (e.g., tumor necrosis factor-alpha, interleukin-1) may be responsible for some changes.

Many seriously ill patients have low levels of thyroid hormones but are not clinically hypothyroid and do not require thyroid hormone supplementation. Patients with euthyroid sick syndrome have low, normal, or only slightly elevated TSH levels, unlike the marked TSH elevations present in true hypothyroidism.