Sick euthyroid sydrome (The Non-Thyroidal Illness Syndrome)

Nonthyroidal Illness Syndrome (NTIS), also known as Sick Euthyroid Syndrome, is a condition commonly observed in seriously ill or malnourished patients. It is characterized by low levels of free triiodothyronine (fT3), typically elevated reverse T3 (rT3), normal or low thyroid-stimulating hormone (TSH), and, if prolonged, low free thyroxine (fT4). NTIS is prevalent among patients in intensive care units (ICUs) and is associated with poor prognosis, particularly when total T4 (TT4) levels drop below 4 µg/dL.

The pathophysiology of NTIS involves several mechanisms:

Suppression of thyrotropin-releasing hormone (TRH) release.
Reduced turnover of T3 and T4.
Decreased hepatic generation of T3.
Increased formation of rT3.
Tissue-specific downregulation of deiodinases, transporters, and thyroid hormone receptors.

Aspect	Details
Definition	Transient alterations in thyroid function tests in critically ill patients.
Prevalence	Present in about 75% of hospitalized patients.
Common Settings	Intensive care units, following major surgeries, severe critical illnesses, and calorie deprivation.
Typical Hormone Patterns	Low total T3 and free T3 levels
	Low or normal T4 levels
	Low or normal TSH levels
Causes	Loss of endogenous hypothalamic input
	Exogenous drug effects
Pathophysiology	Transient alterations in the hypothalamic-pituitary-thyroid axis due to systemic illness.
Clinical Implications	Typically does not require treatment unless thyroid dysfunction persists after recovery...

Try our Free Plan to get the full article.