The
dexamethasone suppression test is designed to
diagnoseDiagnosis is the identification of the nature of anything, either by process of elimination or other analytical methods...
and differentiate among the various types of
Cushing's syndromeCushing's syndrome is a hormone disorder caused by high levels of cortisol in the blood. This can be caused by taking glucocorticoid drugs, or by tumors that produce cortisol or adrenocorticotropic hormone...
and other hypercortisol states.
It has also been used in the research of depression.
DexamethasoneDexamethasone is a potent synthetic member of the glucocorticoid class of steroid hormones. It acts as an anti-inflammatory and immunosuppressant...
is an exogenous steroid that provides negative feedback to the pituitary to suppress the secretion of ACTH. This steroid is unable to pass the blood brain barrier which allows this test to assess a specific part of the
hypothalamic-pituitary-adrenal axisThe hypothalamic-pituitary-adrenal axis , also known as thelimbic-hypothalamic-pituitary-adrenal axis , is a complex set of direct influences and feedback interactions among the hypothalamus , the pituitary gland , and the adrenal glands...
.
The
dexamethasone suppression test is designed to
diagnoseDiagnosis is the identification of the nature of anything, either by process of elimination or other analytical methods...
and differentiate among the various types of
Cushing's syndromeCushing's syndrome is a hormone disorder caused by high levels of cortisol in the blood. This can be caused by taking glucocorticoid drugs, or by tumors that produce cortisol or adrenocorticotropic hormone...
and other hypercortisol states.
It has also been used in the research of depression.
Physiology
DexamethasoneDexamethasone is a potent synthetic member of the glucocorticoid class of steroid hormones. It acts as an anti-inflammatory and immunosuppressant...
is an exogenous steroid that provides negative feedback to the pituitary to suppress the secretion of ACTH. This steroid is unable to pass the blood brain barrier which allows this test to assess a specific part of the
hypothalamic-pituitary-adrenal axisThe hypothalamic-pituitary-adrenal axis , also known as thelimbic-hypothalamic-pituitary-adrenal axis , is a complex set of direct influences and feedback interactions among the hypothalamus , the pituitary gland , and the adrenal glands...
. Specifically, dexamethasone binds to
glucocorticoidGlucocorticoids are a class of steroid hormones that bind to the glucocorticoid receptor , which is present in almost every vertebrate animal cell...
receptors in the basal medial
hypothalamusThe hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland ....
, which lies outside the blood brain barrier, resulting in regulatory modulation.
Interpretation
Low-dose and high-dose variations of the test exist.
The test is given at low (usually 1-2 mg) and high (8 mg) doses of dexamethasone and the levels of
cortisolCortisol is a corticosteroid hormone or glucocorticoid produced by the adrenal cortex, that is part of the adrenal gland . It is usually referred to as the "stress hormone" as it is involved in response to stress and anxiety, controlled by CRH...
are measured to obtain the results.
Low-dose
A normal result is decrease in cortisol levels upon administration of low-dose dexamethasone. Results indicative of Cushing's Disease involve no change in cortisol on low-dose dexamethasone, but inhibition of cortisol on high-dose dexamethasone. If the cortisol levels are unchanged by low- and high-dose dexamethasone then other causes of Cushing's Syndrome must be considered with further work-up necessary.
High-dose
After the high-dose dexamethasone, it may be possible to make further interpretations..
| ACTH |
Cortisol |
Interpretation |
| undetectable or low |
is not suppressed by low or high doses |
Adrenal Cushing syndrome is likely. |
| normal to elevated |
is not suppressed by low or high doses |
Ectopic ACTH syndrome is likely. If an adrenal tumor is not apparent, a chest CT and abdominal CT is indicated to rule out a different tumor secreting ACTH. |
| normal to elevated |
is not suppressed by low doses, but is suppressed by high doses |
Pituitary Cushing syndrome should be considered. A pituitary MRI would be needed to confirm. |
Equivocal results should be followed by a
CRHCorticotropin-releasing hormone , originally named corticotropin-releasing factor , and also called corticoliberin, is a polypeptide hormone and neurotransmitter involved in the stress response....
stimulation testThe ACTH stimulation test is a medical test usually ordered and interpreted by endocrinologists to assess the functioning of the adrenal glands stress response by measuring the adrenal response to adrenocorticotropic hormone...
, with
inferior petrosal sinusThe inferior petrosal sinus, within the human head, is an area beneath the brain, which allows blood veins to span the area, from the center of the head downward. It drains from the cavernous sinus to the sigmoid sinuses above the internal jugular vein. See diagram : labeled under the brain as...
sampling.