Sick Euthyroid Syndrome and Its Relationship to Cortisol Levels and Adrenal Gland Size
Sick euthyroid syndrome does not cause hypocortisolism or adrenal gland enlargement; rather, it is characterized by altered thyroid function tests during acute illness without actual thyroid disease, while cortisol levels are typically elevated in this condition. 1
Understanding Sick Euthyroid Syndrome
Sick euthyroid syndrome (also called euthyroid sick syndrome or non-thyroidal illness syndrome) represents alterations in thyroid function tests that occur during acute or chronic illness in patients without intrinsic thyroid disease:
- Characterized by low serum triiodothyronine (T3), elevated reverse T3, and usually normal or low thyrotropin (TSH) and thyroxine (T4) levels 2
- The severity of thyroid function test abnormalities correlates with illness severity, with low T4 levels predicting poor prognosis 2
- These changes represent a complex mix of physiologic adaptation and pathologic response to acute illness 3
Relationship with Cortisol Levels
Contrary to causing hypocortisolism, sick euthyroid syndrome is typically associated with elevated cortisol levels:
- Patients with severe non-thyroidal illness sufficient to cause low free T4 index and low TSH consistently demonstrate elevated serum cortisol levels (>525 nmol/L) 1
- This cortisol elevation is part of the stress response during acute illness 1
- The presence of elevated cortisol in sick euthyroid syndrome helps differentiate it from pituitary insufficiency, which would present with low cortisol levels 1
Impact on Adrenal Gland Size
There is no evidence in the provided literature that sick euthyroid syndrome causes adrenal gland enlargement:
- None of the guidelines or research papers indicate a relationship between sick euthyroid syndrome and adrenal hypertrophy 4
- Adrenal insufficiency is mentioned as a condition that can interfere with normal TSH levels, but not as a consequence of sick euthyroid syndrome 4
Diagnostic Considerations
When evaluating thyroid function during illness:
- TSH secretion is highly sensitive to factors other than thyroid disorders, including acute illness 4
- Thyroid function tests may be misleading (euthyroid sick syndrome) if performed during acute illness, ketosis, or significant weight loss 5
- Serial TSH measurements are essential to establish that a thyroid disorder is real and persistent 4
- Morning testing is preferred for more accurate results, especially when assessing adrenal function simultaneously 5
Clinical Implications
Understanding the relationship between sick euthyroid syndrome and adrenal function has important clinical implications:
- Supplemental thyroid hormone has not been shown to be beneficial and may be harmful in euthyroid patients with abnormal thyroid function tests due to non-thyroidal illness 6
- Recognition of sick euthyroid syndrome is vital to avoid unnecessary therapy 6
- In patients with heart failure, sick euthyroid syndrome has been associated with worse outcomes but is not an independent negative prognostic factor 7
- Treatment of sick euthyroid syndrome with thyroid hormone to restore normal levels has not shown clear benefits in improving disease prognosis 3
Common Pitfalls to Avoid
- Misinterpreting thyroid function tests during acute illness as primary thyroid dysfunction 5
- Failing to recognize that elevated cortisol levels in sick euthyroid syndrome rule out pituitary insufficiency 1
- Initiating thyroid hormone replacement based on abnormal thyroid function tests during acute illness 6
- Not repeating thyroid function tests after resolution of the acute illness 4