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Euthyroid sick syndrome (ESS), sick euthyroid syndrome (SES), non-thyroidal illness syndrome (NTIS) or low T3 low T4 syndrome is a state of adaptation or dysregulation of thyrotropic feedback control where the levels of T3 and/or T4 are at unusual levels, but the thyroid gland does not appear to be dysfunctional.
This condition is often seen in starvation, critical illness or patients in intensive care unit. The most common hormone pattern in sick euthyroid syndrome is a low total and unbound T3 levels with normal T4 and TSH levels.
Below from
http://www.merckmanuals.com/professional/endocrine_and_metabolic_disorders/thyroid_disorders/euthyroid_sick_syndrome.html
Euthyroid sick syndrome is low serum levels of thyroid hormones in clinically euthyroid patients with nonthyroidal systemic illness. Diagnosis is based on excluding hypothyroidism. Treatment is of the underlying illness; thyroid hormone replacement is not indicated.
Patients with various acute or chronic nonthyroid disorders may have abnormal thyroid function test results. Such disorders include acute and chronic illness, particularly fasting, starvation, protein-energy undernutrition, major trauma, MI, chronic renal failure, diabetic ketoacidosis, anorexia nervosa, cirrhosis, thermal injury, and sepsis.
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. Patients are clinically euthyroid and do not have elevated thyroid-stimulating hormone (TSH) levels.
Pathogenesis is unknown but may include decreased peripheral conversion of T4 to T3, decreased clearance of rT3 generated from T4, and decreased binding of thyroid hormones to thyroxine-binding globulin (TBG). Proinflammatory cytokines (eg, tumor necrosis factor-α, IL-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 and amiodarone , which impairs the peripheral conversion of T4 to T3, and by drugs such as dopamine and corticosteroids, which decrease pituitary secretion of TSH, resulting in low serum TSH levels and subsequent decreased T4 secretion.
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Diagnosis
The diagnostic dilemma is whether the patient has hypothyroidism or euthyroid sick syndrome. The best test is measurement of TSH, which in euthyroid sick syndrome is low, normal, or slightly elevated but not as high as it would be in hypothyroidism. Serum rT3 is elevated, although this measurement is rarely done. Serum cortisol is often elevated in euthyroid sick syndrome and low or low-normal in hypothyroidism due to pituitary-hypothalamic disease. Because tests are nonspecific, clinical judgment is required to interpret abnormal thyroid function tests in the acutely or chronically ill patient. Unless thyroid dysfunction is highly suspected, thyroid function tests should not be ordered for patients in the ICU.
Treatment
Treatment with thyroid hormone replacement is not appropriate. When the underlying disorder is treated, results of thyroid tests normalize.
