Test of choice for diagnosing Cushing’s syndrome: (LQ)
|A||Overnight high dose Dexamethasone suppression test|
|B||Low dose Dexamethasone suppression test|
|C||Corticotrophin releasing hormone test|
|D||Insulin tolerance test|
Low dose Dexamethasone suppression test
Investigation of Suspected Cushing’s syndrome
1). The diagnosis of Cushing's syndrome depends on the demonstration of increased cortisol production and failure to suppress cortisol secretion normally when dexamethasone is administered.
2). Once the diagnosis is established, further testing is designed to determine the etiology.
3). Confirm the diagnosis (a raised cortisol) & then localize the source on the basis of laboratory testing.
(Ref. Hari-18th ed., Fig, 342.9 Pg- 2947)
Recent advances: New algorithm for diagnosis of Cushing syndrome.
Note: Algorithm has changes as compared to 17th edition!!!
Diagnosis: The diagnosis of Cushing’s syndrome depends on the demonstration of increased cortisol production and failure to suppress.
a. Increase 24h urinary free cortisol
b. Dexamethasone (DM) suppression test
i. Low dose DM suppression test is done to differentiate between Cushing syndrome and simple obesity.
ii. High dose suppression test is done to differentiate between Cushing syndrome due to pituitary adenoma and ectopic secretion of ACTH