Non-Thyroidal Illness: Physiopathology and Clinical Implications

In critical illness, several abnormalities in thyroid hormone (TH) secretion, metabolism and action have been described in patients without previous diagnosis of intrinsic thyroid disease and are collectively called “Non thyroidal syndrome” (NTIS) [1]; this term is now largely employed, in the place of “euthyroid sick syndrome” [2-4] or “low-T3 syndrome”, due to the most common abnormality, a decreased level of serum total triiodothyronine (T3), which can be detected very early, within 2 hours after the onset of severe physical stress [5-7]. However, T3 lowering is only one of the endocrine picture described is such a situation; therefore the term NTIS seems to be more appropriate, also strengthening its extrathyroidal source.