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Pituitary-thyroid dysfunction in severe non-thyroidal disease: "low-T4 syndrome"
Endokrinologie
|October 1, 1982
Summary
Critically ill patients often exhibit low thyroxine (T4) levels, a condition distinct from primary hypothyroidism. This "low-T4 syndrome" indicates a poor prognosis and is linked to impaired thyroid-stimulating hormone (TSH) release due to severe illness.
Area of Science:
- Endocrinology
- Critical Care Medicine
- Internal Medicine
Background:
- Thyroid function is frequently altered in critically ill patients.
- Distinguishing between "low-T4 syndrome" and true hypothyroidism is clinically significant.
Purpose of the Study:
- To investigate thyroid function test results in intensive care unit (ICU) patients.
- To differentiate "low-T4 syndrome" from primary hypothyroidism in severe non-endocrine diseases.
Main Methods:
- Assessed thyroid function tests (serum thyroxine, triiodothyronine, thyroxine-binding globulin, reverse triiodothyronine) in 335 ICU patients.
- Evaluated thyroid-stimulating hormone (TSH) secretion response to intravenous thyrotropin-releasing hormone (TRH) in 20 patients with severe non-endocrine diseases and low thyroxine levels.
Main Results:
- Twenty patients with severe non-endocrine diseases presented with serum thyroxine levels in the hypothyroid range.
- Reduced serum concentrations of total thyroxine, triiodothyronine, and thyroxine-binding globulin were observed.
- TSH secretion response to TRH was variable (normal, lowered, or absent), excluding primary hypothyroidism.
Conclusions:
- Decreased thyroid hormone levels in critically ill patients, termed "low-T4 syndrome," are common.
- Impaired TSH responsiveness to TRH likely results from illness-induced inhibition of pituitary TSH release.
- This syndrome is an indicator of poor prognosis and must be differentiated from true hypothyroidism based on clinical presentation and disease course.