Dexamethasone suppression test

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Dexamethasone suppression test
Diagnostics
Dexamethasone structure.svg
 
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Dexamethasone suppression test
Diagnostics
Dexamethasone structure.svg
proopiomelanocortin derivatives
POMC
   
γ-MSHACTHβ-lipotropin
     
 α-MSHCLIPγ-lipotropinβ-endorphin
    
  β-MSH 


Physiology[edit]

Dexamethasone is an exogenous steroid that provides negative feedback to the pituitary to suppress the secretion of ACTH and CRH. Specifically, dexamethasone binds to glucocorticoid receptors in the pituitary gland, which lies outside the blood brain barrier, resulting in regulatory modulation.[1]

Interpretation[edit]

Low-dose and high-dose variations of the test exist.[2]

The test is given at low (usually 1–2 mg) and high (8 mg) doses of dexamethasone and the levels of cortisol are measured to obtain the results.[3]

A low dose dexamethasone suppresses cortisol in individuals with no pathology in endogenous cortisol production. A high dose dexamethasone exerts negative feedback on pituitary ACTH producing cells but not on ectopic ACTH producing cells or adrenal adenoma.

Low-dose[edit]

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[edit]

After the high-dose dexamethasone, it may be possible to make further interpretations.[4]

ACTH†CortisolInterpretation
undetectable or lowis not suppressed by high or low doses.Primary Hypercortisolism is likely.
normal to elevatedis not suppressed by high or low dosesEctopic 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.
Highis not suppressed by low doses, but is suppressed by high dosesCushing's disease should be considered. This is because the pituitary still retains some feedback control. A pituitary MRI would be needed to confirm.

†ACTH as measured prior to dosing of dexamethasone[5]

Equivocal results should be followed by a CRH stimulation test, with Inferior petrosal sinus sampling.

References[edit]

  1. ^ Cole MA, Kim PJ, Kalman BA, Spencer RL (February 2000). "Dexamethasone suppression of corticosteroid secretion: evaluation of the site of action by receptor measures and functional studies". Psychoneuroendocrinology 25 (2): 151–67. doi:10.1016/S0306-4530(99)00045-1. PMID 10674279. 
  2. ^ Isidori AM, Kaltsas GA, Mohammed S, et al (November 2003). "Discriminatory value of the low-dose dexamethasone suppression test in establishing the diagnosis and differential diagnosis of Cushing's syndrome". J. Clin. Endocrinol. Metab. 88 (11): 5299–306. doi:10.1210/jc.2003-030510. PMID 14602765. 
  3. ^ Medline Plus "Dexamethasone suppression test"
  4. ^ Kumar, Abbas, Fausto. Robbins and Cotran Pathologic Basis of Disease, 7th ed. Elsevier-Saunders; New York, 2005
  5. ^ Longo, Dan L.; Fauci, Anthony S.; Kasper, Dennis L.; Hauser, Stephen L.; Jameson, J. Larry; Loscalzo, Joseph (2012), Harrison's Principles of Internal Medicine (18th ed.), McGraw Hill Medical, pp. 2897–2898, ISBN 978-0-07174889-6