Cushing's Syndrome

1. Cushing's syndrome results from the chromic exposure to excess glucocorticoid hormone
2. Glucocorticoid excess may be secondary to increased endogenous production of cortisol or to exogenous ingestion of glucocorticoids

• The most common endogenous cause in adults is bilateral adrenal hyperplasia secondary to excessive secretion of ACTH by the pituitary
• In approximately 90% of the cases, the excessive secretion of ACTH by the pituitary is due to an adenoma
• The adenoma is usually insidious with a female to male ratio of 5:1
• Another endogenous cause may be an adrenal tumor

1. Clinical manifestations

• Obesity with characteristic 'buffalo hump', moon facies
• Muscle wasting
• Osteoporosis
• Abdominal Striae
• Depression
• Hirsutism

1. Diagnosis . The diagnosis is a two step approach:

• First you must obtain a cortisol level in the patient to verify the patient does have hypercortisolism
• Next, the 24 hour urinary excretion of cortisol is measured:
• dexamethasone, 1mg is taken po by the patient between 11pm and midnight
• next am a fasting blood cortisol level is obtained
• Results
• In the patient without cushing's, the dexamethasone will suppress cortisol production to ,5mcg/dL
• If blood cortisol level is .5mcg/dL, this is consistent with cushing's syndrome
• False positive results may occur if:
• the patient is under stress
• the patient is in renal failure
• the patient has a history of alcoholism
• the patient is depressed

1. Once cushing's syndrome is established, the high-dose dexamethasone suppression test should be performed to determine the etiology

• High-dose dexamethasone
• dexamethasone 2mg is taken po by the patient q6 for two days or a one time dose of 8mg may be taken
• at the end of the two day period, blood cortisol, urinary free cortisol, or urinary metabolites (17-hydroxy corticosteroids, 17-ketogenic steroids) are measured
• Results
• little or no suppression of cortisol by dexamethasone is consistent with an adrenal tumor
• suppression by at least 50% is consistent with an ACTH- producing pituitary adenoma

References:

1. Cecil's Essentials of Medicine, 3rd ed.
2. ABC's of Interpretive Laboratory Medicine, 3rd. ed.; Bakerman

Last Modified: 11/1/95
Copyright © 1995 University of Texas - Houston Medical School, DPALM MEDIC, All rights reserved.