What causes euthyroid sick syndrome?

Updated: Aug 28, 2020
  • Author: Serhat Aytug, MD; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Multiple explanations have been proposed for the causes of NTI, including the following:

  • Accuracy of test assays in NTI

  • Cytokines

  • Deiodination

  • Inhibition of TRH and TSH secretion

  • Inhibition of plasma membrane transport of iodothyronines

  • Thyroid-binding globulin decrease/desialation

  • Reduction in TR expression as well as DNA binding

  • Drugs that influence thyroid function

A study by Petrone et al indicated that euthyroid sick syndrome can result from obstructive sleep apnea (OSA) with severe nocturnal hypoxemia. The syndrome was found in 13 out of 125 patients in the study (10.4%) with moderate to severe OSA but occurred in none of the controls. Mean nocturnal oxygen saturation was worse in persons with euthyroid sick syndrome than in other OSA patients. Treatment of OSA resulted in a rise in free T3 to normal range. [18]

The aforementioned study by Wang et al reported that independent risk factors for CABG-associated euthyroid sick syndrome include advanced age, a higher EuroSCORE II value, and moderate and poor left ventricular ejection fraction. [17]

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