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Thyroid axis in patients with Cushing's syndrome
Archives of Internal Medicine
|July 1, 1979
Summary
Cushing's syndrome alters thyroid hormone levels, reducing triiodothyronine (T3) and blunting the thyrotropin (TSH) response to protirelin. This indicates the protirelin test is unreliable for assessing thyroid function in these patients.
Area of Science:
- Endocrinology
- Thyroid Research
- Metabolic Disorders
Background:
- Cushing's syndrome is characterized by excess cortisol, potentially affecting thyroid hormone metabolism.
- Thyroid hormone levels and the pituitary-thyroid axis regulation are crucial for metabolic homeostasis.
Purpose of the Study:
- To evaluate thyroid hormone profiles and thyrotropin (TSH) response to protirelin in patients with Cushing's syndrome.
- To determine the diagnostic utility of the protirelin stimulation test in the presence of hypercortisolism.
Main Methods:
- Assessed serum thyroxine (T4), free T4, triiodothyronine (T3), and free T3 levels.
- Administered intravenous protirelin (400 micrograms) and measured TSH response at 20 and 60 minutes.
- Compared results between ten patients with Cushing's syndrome and ten matched healthy controls.
Main Results:
- Patients with Cushing's syndrome exhibited mildly depressed T4 and significantly reduced T3 and free T3 levels compared to controls.
- The TSH response to protirelin was markedly blunted in Cushing's syndrome patients (3.3-2.6 microU/mL) versus normal subjects (12.3-10.7 microU/mL).
- Reduced peripheral conversion of T4 to T3 was attributed to glucocorticoid excess.
Conclusions:
- Glucocorticoid excess in Cushing's syndrome suppresses peripheral T3 production, leading to lower T3 and free T3 levels.
- The protirelin stimulation test has limited value in assessing thyroid status in Cushing's syndrome due to blunted TSH response.
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