Test of choice for diagnosing cushings syndrome: September 2011
Correct Answer: Overnight low dose Dexamethasone suppression test
Description: Ans. B: Overnight low dose Dexamethasone suppression test Initial investigation in suspected cases of Cushing's syndrome is Overnight-low dose Dexamethasone suppression test Cushings syndrome/ Hypercoisolism: It should be suspected in cases of: - Hypeension of recent onset, - dermal striae, - easy bruisability, - evidence of glucose intolerance (glycosuria) Other manifestations: - Osteoporosis, muscle weakness, - psychogenic alterations, - hirsutism, - granulocytic leukocytosis with lymphopenia 80% cases are due to pituitary tumour which secretes ACTH, resulting in adrenal hyperplasia First step to perform is the dexamethasone suppression test, which consists of administering 1 mg of dexamethasone at 11 pm, and then measuring serum coisol levels in a blood sample drawn at 8 am next day. Abnormal high coisol levels after this test confirms hypercoisolism The nest step is to find the source of excessive coisol or ACTH Baseline plasma ACTH measurement should be performed after a diagnosis of hypercoisolism has been confirmed by dexamethasone suppression test. This checks whether the excessive coisol production is secondary to increased ACTH levels scan of the chest and abdomen are performed to look for ectopic sources of ACTH
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