Non-thyroidal Illness Syndrome

Abstract

NTIS refers to a syndrome found in seriously ill or starving patients with low fT3, usually elevated RT3, normal or low TSH, and if prolonged, low fT4. It is found in a high proportion of patients in the ICU setting, and correlates with a poor prognosis if TT4 is <4ug/dl. The patho-physiology includes suppression of TRH release, reducedT3 and T4 turnover, reduction in liver generation of T3, increased formation of RT3, and tissue specific down-regulation of deiodinases, transporters, and TH receptors. Although long debated, tissue TH levels are definitely reduced, and tissue hypothyroidism is presumably present. This is often not clinically evident because of the brief duration, and reduced but not absent tissue levels of TH. Although recognized for nearly 4 decades, interpretation of the syndrome is contested, because of lack of data. Some observes, totally without data, argue that it is a protective response and should not be treated. Other observers (as in this review) present available data suggesting, but not proving, that thyroid hormone replacement is appropriate, not harmful, and may be beneficial. The best form of treatment (TRH,TSH,or T3+T4) and possible accompanying treatments (GHRH, Cortisol, nutrition, insulin) lack consensus. In this review current data are laid out for reader's review and judgment.