• Description
  • A change in thyroid hormone levels (typically decreased) that occurs in severe illness or severe physical stress
  • Common in intensive care patients and associated with morbidity and mortality
  • Also known as euthyroid sick syndrome (ESS)
• Pathophysiology: multifactorial and not fully understood
  • Thyroid gland function typically remains normal.
  • Cytokines (e.g., interleukin 6) are thought to cause various changes in levels of circulating TSH and thyroid hormones.
  • Altered deiodinase enzyme activity leads to:
    • ↓ Conversion of T4 to T3
    • ↑ Conversion of T4 to reverse T3 (rT3) by thyroxine 5-monodeiodinase
  • Various factors, e.g., protein loss due to nephrotic syndrome, may also lead to decreased levels of thyroid-binding globulin.
• Clinical features
  • Signs and symptoms of the underlying illness
  • Typically no classic symptoms of hyper- or hypothyroidism
• Diagnostics
  • Early: Low T3, normal TSH & T4
  • Late: Low T3, TSH & T4