Endocrine Function III Part 3
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Overnight Dexamethasone Suppression Test (screening test) -Principle
Feedback mechanism of hypersecretion can be tested by administering a potent glucocorticoid and judging suppression of ACTH secretion by measuring serum or urine cortisol levels
What is the clinical use of the corticotropin releasing hormone (CRH) test?
Differentiates secondary (pituitary) and tertiary (hypothalamic) adrenal sufficiency
Overnight Dexamethasone Suppression Test (screening test) -Diagnostic Use
Differentiate normal patient from Cushing’s syndrome, either due to Cushing’s disease, adrenal tumor, or ectopic ACTH syndrome
Overnight Dexamethasone Suppression Test (screening test) -expected normal response
decreased cortisol (<3 ug/dL)
Overnight Dexamethasone Suppression Test (screening test) -cause of abnormal results
increased cortisol (>10 ug/dL) = Cushing’s Syndrome
Which causes of Cushing’s syndrome may be differentiated using the high-dose test?
adrenal tumors, nonendocrine ACTH-secreting tumors, and pituitary Cushing’s disease
What do normal results look like in high dose dexamethasone suppression test look like?
50% suppression of cortisol production
How do abnormal results differ in Cushing’s and adrenal/ectopic tumors during the high dose test?
Cushing’s = most suppress cortisol production Adrenal/ectopic tumors = no change in cortisol levels
Name the three principle hormones classified as catecholamines and their sites of synthesis.
1 epinephrine (80-90% medulla production) 2 norepinephrine (10-20% medulla production) 3 dopamine (small amount produced in adrenal medulla)
These catecholamines have a marked influence on the vascular system.
dopamine and norepinephrine
This catacholamine influences metabolic processes, especially carbohydrate metabolism.
epinephrine
This catecholamine inhibits phenylethanolamine-N-methyltransferase
epinephrine
This catecholamine inhibits tyrosine hydroxylase.
Norepinephrine
What is the cause of pheochromocytomas?
tumor in adrenal medulla, too much catecholamines
What is the principle clinical symptom of pheochromocytomas?
hypertension
What is the best specific urine screening test for pheochromocytomas?
urinary metanephrines
What is the best diagnostic test for pheochromocytomas?
urinary VMA
What is the commonly affected age group of neuroblastomas?
pediatric
What are the clinical symptoms for neuroblastomas?
tumor in or near adrenal gland producing a lot of dopamine, causing transient hypertension and tachycardia
What is the best specific urine screening test for neuroblastomas?
urinary homovanillic acid (HVA) (diagnostic)