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File:Dexamethasone structure.png

Dexamethasone

Template:POMC The dexamethasone suppression test is designed to diagnose and differentiate among the various types of Cushing's syndrome and other hypercortisol states.[1]

It has also been used in the research of depression.[2]

Physiology

Dexamethasone 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 axis. Specifically, dexamethasone binds to glucocorticoid receptors in the basal medial hypothalamus, which lies outside the blood brain barrier, resulting in regulatory modulation.[3]

Interpretation

Low-dose and high-dose variations of the test exist.[4]

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.[5]

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.[6].

ACTH Cortisol Interpretation
undetectable or low is not suppressed by low or high doses Primary 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 Cushing disease should be considered. A pituitary MRI would be needed to confirm.

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

References

  1. Medline Plus "Dexamethasone suppression test"
  2. Fountoulakis KN, Gonda X, Rihmer Z, Fokas C, Iacovides A (2008). "Revisiting the Dexamethasone Suppression Test in unipolar major depression: an exploratory study". Ann Gen Psychiatry 7: 22. doi:10.1186/1744-859X-7-22. PMC 2590593. PMID 19014558.
  3. 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. http://linkinghub.elsevier.com/retrieve/pii/S0306-4530(99)00045-1.
  4. 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. http://jcem.endojournals.org/cgi/pmidlookup?view=long&pmid=14602765.
  5. Medline Plus "Dexamethasone suppression test"
  6. Kumar, Abbas, Fausto. Robbins and Cotran Pathologic Basis of Disease, 7th ed. Elsevier-Saunders; New York, 2005

Template:Pathology-stub Template:Endocrine system procedures ar:فحص التثبيط بالديكساميثازون de:Dexamethason-Suppressionstest es:prueba de la supresión de la dexametasona pl:Test hamowania z deksametazonem

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