Cushing's syndrome is a non-specific name for any source of excessive glucorticoids. There are four main causes:

1) Exogenous glucocorticoids

2) Pituitary Cushing’s syndrome known as Cushing’s disease, due to a pituitary adenoma secreting excessive ACTH

3) Ectopic production of ACTH. Two varieties; one due to malignant tumours usually of the lung , these patients present with hypertension, hypokalaemia and hyperpigmentation. The second type is due to carcinoid tumours.

In the dexamethasone suppression test normal individuals suppress cortisol levels to <

50 nmol/L.