Final answer:
Euthyroid sick syndrome (ESS) refers to a condition in which thyroid hormone levels appear normal, but the body's response to those hormones is altered due to a non-thyroidal illness. It is commonly seen in critically ill patients and is a transient condition that resolves as the underlying illness improves.
Step-by-step explanation:
Euthyroid sick syndrome (ESS) refers to a condition in which thyroid hormone levels appear to be normal, but the body's response to thyroid hormones is altered due to a non-thyroidal illness. In ESS, the thyroid function tests may show normal thyroid hormone levels or slight variations, but the patient may exhibit symptoms of hypo- or hyperthyroidism.
ESS is commonly seen in critically ill patients, such as those with severe infections, trauma, or other systemic illnesses. The altered thyroid hormone metabolism in ESS is believed to be a protective mechanism that helps the body conserve energy and redirect resources towards fighting the underlying illness.
It is important to note that ESS is a transient condition and the thyroid function usually improves as the underlying illness resolves.