Euthyroid Sick Syndrome, also known as non-thyroidal illness syndrome (NTIS) or low T3 syndrome, refers to a dysfunctional thyroid hormone state that occurs in individuals who are critically ill or have severe systemic diseases, without any underlying thyroid gland dysfunction. It is characterized by alterations in the levels of thyroid hormones, particularly a decrease in the active hormone triiodothyronine (T3), while the levels of free thyroxine (T4) and thyroid-stimulating hormone (TSH) remain within or close to the normal range.
During periods of severe illness or stress, the body's physiological response is to downregulate the production of active thyroid hormone, T3, to preserve energy, redirect resources, and prioritize the healing process. This response is believed to be mediated by various mechanisms, including alterations in the hypothalamic-pituitary-thyroid axis, decreased binding of thyroid hormone to carrier proteins, and changes in the peripheral metabolism of thyroid hormones.
Euthyroid Sick Syndrome is commonly seen in critically ill patients in intensive care units, those with severe infections, burn victims, post-surgical patients, and individuals with chronic systemic illnesses such as heart failure, liver disease, or kidney failure. The presence of euthyroid sick syndrome is associated with worse outcomes in these patients, including increased mortality rates and prolonged hospital stays.
Treatment of euthyroid sick syndrome involves focusing on the underlying cause of the illness or disease and providing supportive care. In most cases, thyroid hormone replacement therapy is not recommended, as the underlying dysfunction is not due to thyroid gland failure. However, further research is needed to fully understand the implications of euthyroid sick syndrome and its management in different clinical scenarios.
