Euthyroid sick syndrome, sick euthyroid syndrome, non-thyroidal illness syndrome 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.
Causes of euthyroid sick syndrome include a number of acute and chronic conditions, including pneumonia, fasting, starvation, sepsis, trauma, cardiopulmonary bypass, malignancy, stress, heart failure, hypothermia, myocardial infarction, chronic renal failure, cirrhosis, and diabetic ketoacidosis.
Ill patients may have normal, low, or slightly elevated TSH depending on the spectrum of illness. Total T4 and T3 levels may be altered by binding protein abnormalities, and medications. Reverse T3 are generally increased signifying inhibition of normal Type 1 enzyme or reduced clearance of reverse T3. Generally the levels of Free T3 will be lowered, followed by the lowering of Free T4 in relation to severity of the disease. Patients might have high corticosteroid level.
Several trials investigated a possible therapy of ESS. However, they yielded inconsistent and partly contradictory results. This may be caused in the fact that the investigated populations were too heterogeneous in the lack of a consistent definition of non-thyroid illness syndrome..
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