Cushing's

Question 1

ACTH dependent causes

Answer 1

Cushing’s disease (80%): pituitary tumour secreting ACTH producing adrenal hyperplasia
ectopic ACTH production (5-10%): e.g. small cell lung cancer is the most common causes

Question 2

ACTH independent causes

Answer 2

iatrogenic: steroids
adrenal adenoma (5-10%)
adrenal carcinoma (rare)
Carney complex: syndrome including cardiac myxoma
micronodular adrenal dysplasia (very rare)

Question 3

Pseudo-Cushing’s

Answer 3

mimics Cushing’s
often due to alcohol excess or severe depression
causes false positive dexamethasone suppression test or 24 hr urinary free cortisol
insulin stress test may be used to differentiate

Question 4

VBG finding

Answer 4

hypokalaemic metabolic alkalosis + impaired glucose tolerance

Question 5

Cushing’s test

Answer 5

The three most commonly used tests are:
overnight (low-dose) dexamethasone suppression test
this is the most sensitive test and is now used first-line to test for Cushing’s syndrome
patients with Cushing’s syndrome do not have their morning cortisol spike suppressed
24 hr urinary free cortisol
two measurements are required
bedtime salivary cortisol
two measurements are required

Question 6

High-dose dexamethasone suppression test: Cortisol not suppressed + ACTH suppressed

Answer 6

Cushing’s syndrome due to other causes (e.g. adrenal adenomas)

Question 7

High-dose dexamethasone suppression test: Cortisol suppressed + ACTH suppressed

Answer 7

Cushing’s disease (i.e. pituitary adenoma → ACTH secretion)

Question 8

High-dose dexamethasone suppression test: Cortisol not suppressed + ACTH not suppressed

Answer 8

Ectopic ACTH syndrome