Chapter 45 - Euthyroid sick syndrome

Abstract

Euthyroid sick syndrome, also known as nonthyroidal illness syndrome, is a group of changes in serum thyroid-stimulating hormone (TSH) and thyroid hormone levels that are seen in a variety of nonthyroidal illnesses and result primarily from circulating cytokines and inflammatory mediators that interfere with thyroid hormone production, metabolism, and action at multiple levels. The magnitude of the TSH and thyroid hormone changes is proportional to the severity of the underlying nonthyroidal illness. Transient elevation of serum TSH is often seen as patients recover from a nonthyroidal illness. Euthyroid sick 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.