Cushing's Syndrome

Question 1

Name some ACTH dependent causes of Cushing’s Syndrome

Answer 1

Cushing’s disease (80%)
- pituitary tumour secreting ACTH producing

Ectopic ACTH production (5-10%):
- e.g. small cell lung cancer

Question 2

Name some ACTH independent causes of Cushing’s syndrome

Answer 2

• Iatrogenic => steroids
• adrenal adenoma (5-10%)
• adrenal carcinoma (rare)
• Carney complex: syndrome including cardiac myxoma
  micronodular adrenal dysplasia

Question 3

What can cause pseudo Cushings?

Answer 3

alcohol excess or severe depression

Question 4

What findings may be present on a blood gas in Cushing’s Syndrome?

Answer 4

• Hypokalaemic metabolic alkalosis
• impaired glucose tolerance.

Question 5

Ectopic ACTH secretion (e.g. secondary to small cell lung cancer) is characteristically associated with very low potassium levels. TRUE/FALSE?

Answer 5

TRUE

Question 6

What investigations can be used to confirm Cushing’s Syndrome?

Answer 6

1) overnight (low-dose) dexamethasone suppression test
- no suppression of morning cortisol spike in Cushings

2) 24 hr urinary free cortisol

3) bedtime salivary cortisol

Question 7

If cortisol is NOT suppressed and ACTH is suppressed following a dexamethasone suppression test, what does this indicate?

Answer 7

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

Question 8

If both cortisol and ACTH are suppressed following a low-dose dexamethasone suppression test, what does this indicate?

Answer 8

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

Question 9

If neither cortisol or ACTH are suppressed following a low-dose dexamethasone suppression test, what does this indicate?

Answer 9

Ectopic ACTH syndrome

Question 10

What test can be used to differentiate between Cushing’s and Pseudo-cushings?

Answer 10

An insulin stress test