Nonthyroidal Illness Syndrome

Abstract

Although the pathophysiology of thyroid hormone changes observed in acute or chronic diseases is not clearly understood, it has been known for about the last 50 years that the body has an adaptive metabolic response. On the other hand, it has also been shown in many studies that it can make inferences about the prognosis of the primary underlying disease. The most known of this thyroid hormone change pattern, defined as a non-thyroid disease, are low triiodothyronine (T3) and increased reverse T3 (rT3) levels. Although many pathogenetic mechanisms are thought to lead to these changes, the most known are changes in deiodinase activity, thyrotropin (TSH) secretion, and serum carrier proteins and/or cellular carrier receptors. Changes in thyroid hormones can vary at different stages of the primary underlying disease. In addition, in different clinical conditions or pathologies, thyroid hormones are affected in different ways, causing difficulty in the differential diagnosis. Many drugs used in the clinic are also known to affect thyroid hormones at different levels and directions. Current conditions should be taken into account when evaluating, and if possible, a full panel of thyroid hormones, especially TSH with free thyroxine (sT4), should be seen. The need for treatment should be decided by taking into account laboratory findings as well as the patient's clinical presentation and history. In many studies, routine thyroid hormone replacement is not recommended, as it does not give a positive or negative net result.

Keywords

• euthyroid sick syndrome
• pathogenesis
• differential diagnosis
• treatment
• prognosis