Cushing’s Disease

It should be noted that exogenous causes of Cushing's syndrome (e.g. glucocorticoid therapy) are far more common than endogenous ones.

ACTH dependent causes

• 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

ACTH independent causes

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

Pseudo-Cushing's

• 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

Investigations

This section will consider: