From the Research
Euthyroid sick syndrome, also known as non-thyroidal illness syndrome, is a condition where patients with acute or chronic non-thyroidal illnesses have abnormal thyroid function tests despite not having intrinsic thyroid disease, and the focus should be on treating the underlying condition causing the syndrome rather than the thyroid abnormality itself. This syndrome typically presents with low T3 levels, normal or low T4, and normal or slightly decreased TSH. The pathophysiology of euthyroid sick syndrome is complex and involves alterations in the iodothyronine deiodinases, thyroid-stimulating hormone secretion, thyroid hormone binding to plasma protein, transport of thyroid hormone in peripheral tissues, and thyroid hormone receptor activity 1.
The abnormal thyroid function tests in euthyroid sick syndrome are thought to be an adaptive response to illness, with the body decreasing conversion of T4 to T3 as a mechanism to conserve energy, and inflammatory cytokines affecting the hypothalamic-pituitary-thyroid axis 2. The degree of thyroid function impairment correlates with disease severity, and low levels of thyroid hormones, particularly thyroxine, predict a poor prognosis 3.
Key Points
- No specific treatment is required for euthyroid sick syndrome itself, as it represents an adaptive response to illness rather than a primary thyroid disorder.
- Thyroid hormone replacement therapy is generally not recommended unless there is clear evidence of primary hypothyroidism, as administering thyroid hormones in this setting has not been shown to improve outcomes and may potentially be harmful 4.
- The abnormal thyroid function tests typically normalize once the patient recovers from the underlying illness.
- Regular monitoring of thyroid function is reasonable during recovery, but intervention is rarely needed.
Treatment Approach
The focus should be on treating the underlying condition causing the syndrome, whether it's severe infection, major trauma, burns, or critical illness. Treatment of the euthyroid sick syndrome with thyroid hormone to restore normal serum thyroid hormone levels in an effort to improve disease prognosis and outcomes continues to be a focus of many clinical studies, although currently available data do not provide evidence of a clear benefit of treatment 1.