Non-thyroidal Illness Syndrome (Euthyroid Sick Syndrome)

Non-thyroidal illness syndrome, also known as euthyroid sick syndrome, is a series of changes in serum TSH and thyroid hormone levels that are seen in a variety of non-thyroidal illnesses and result primarily from circulating cytokines and inflammatory mediators that interfere with thyroid hormone production, transport, metabolism, and action at multiple levels. The magnitude of the TSH and thyroid hormone changes is proportional to the severity of the underlying non-thyroidal illness. Transient elevation of serum TSH is often seen as patients recover from a nonthyroidal illness. Non-thyroidal illness syndrome appears to be an adaptive response to reduce tissue metabolism and preserve energy during systemic illnesses; therefore, treatment with thyroid hormone is not generally recommended but may be beneficial in patients with chronic heart failure.