Cushing's

Question 1

What is cushing’s?

Answer 1

Prolonged and abnormal elevation of cortisol

Moon face
Central obesity
Abdominal striae
Buffalo hump
Proximal limb muslce wasting

Question 2

Cushing’s syndrome LOW DOSE TEST

Answer 2

1. give 1mg dexamethasone at 10pm (<50 cortisol is normal)
2. measure the cortisol and ACTH at 9am

the low dose tests confirm a normal response OR Cushing syndrome

normal- the low dose 1g of dexamethasone will suppress CRH and ACTH so cortisol will be LOW

in Cushing syndrome, the 1mg is not enough to overcome the high cortisol so cortisol remains HIGH

Question 3

Cushing’s syndrome HIGH DOSE TEST

Answer 3

once Cushing syndrome is confirmed

1. give 8mg dexamethasone

in pituitary adenoma, the 8mg dex is enough to suppress the ACTH (and cortisol). ACTH low, Cortisol low

in adrenal adenoma, the dexamethasone can suppress CRH/ACTH but cortisol is being produced independently. remains HIGH. ACTH low, Cortisol high

in ectopic ACTH the dexamethasone cannot suppress the ectopic ACTH as it’s being produced elsewhere.
ACTH high, Cortisol high

Question 4

Cushing investigatoin

Answer 4

low dose test
high dose test
24-hour urinary free cortisol

FBC (WCC) (K low if aldosterone is being released by an adrenal adenoma)
MRI pituitary adenoma
Chest CT lung cancer
Abdominal CT- adrenal tumour

Question 5

dexamethasone supression test (overnight 1mg) false +ve

Answer 5

overnight 1mg at 11pm
one dose

false positive results (pseudo)
- severe obesity or depression due to glucocorticoid resistance
- enzyme inducing drugs (metabolise dexamethasone more quickly)
- dialysis / systemic illness
- women on oestrogen therapy
- chronic alcohol excess
proceed to 48hr dexamethasone suppression test.

Question 6

48 hour test low dose (0.5mg) high dose (2mg)

Answer 6

given at 9am 6 hourly
eight doses

serum cortisol is measured at 9am at the start and end of day