Euthyroid Sick Syndrome

Euthyroid sick syndrome (non thyroidal illness syndrome) is abnormal thyroid function tests in acute or chronic illness without primary thyroid or pituitary disease.

• Occurs in up to 70% of ICU patients and many hospitalised patients.
• Mechanisms: reduced T4 to T3 conversion (type 1 deiodinase inhibition), increased reverse T3, reduced TSH secretion, cytokine effects, starvation, drugs (glucocorticoids, dopamine, amiodarone).
• Stages: low T3 (mild illness), low T3 and T4 with low TSH (severe), recovery phase with transient TSH rise up to 20 mIU/L.
• Low T4 predicts poor prognosis.

• No features of thyroid disease; presentation is that of the underlying illness.
• Absence of goitre or thyroid symptoms before illness.

• Low total and free T3, high reverse T3, normal or low T4, TSH low, normal or transiently high.
• Avoid thyroid testing in acutely ill patients unless thyroid disease is suspected.
• Repeat tests 4 to 6 weeks after recovery.
• Distinguish from central hypothyroidism (pituitary disease, other hormone deficits).

• Treat the underlying illness; do not give thyroid hormone (no outcome benefit, possible harm).
• Exception: clinical myxoedema or established hypothyroidism.
• Recheck thyroid function after resolution, with treatment only if abnormalities persist.