Sick euthyroid syndrome: A myth or reality

Abstract

Altered thyroid function in non-thyroidal illness(NTI) is a well-recognized finding. The term euthyroid sick syndrome (SES) identifies abnormalities in thyroid function observed in patients with systemic nonthyroidal illnesses (NTIs). SES being most common endocrine change seen in critically ill patients, is characterized by low triiodothyronine (T3), low or normal thyroxine (T4) and normal thyroid stimulating hormone (TSH). The extent of SES is associated with prognosis, but no proof exists for causality of this association. T3 levels reflect the patient’s clinical status, T4 levels can predict survival. Initially, SES is a consequence of the acute phase response to systemic illness and macro- nutrient restriction, which might be beneficial. Pathogenesis of SES in long term critical illness is more complex and includes suppression of hypothalamic thyrotropin-releasing hormone, accounting for persistently reduced secretion of thyroid-stimulating hormone despite low plasma thyroid hormone. Distinguishing between SES and other primary thyroid disorders, can be difficult in ICU setting. Clinical benefits of supplementing thyroid hormone in SES has not been answered adequately. No evidence-based consensus or guideline advocates thyroid hormone treatment of SES at present.

Keywords

• sick euthyroid syndrome
• non-thyroidal illness
• thyroid hormone
• critical illness