The most common cause of cortisol excess is the therapeutic administration of synthetic steroids (iatrogenic)
Cushing's disease is when the increased cortisol levels are caused by a functioning pituitary adenoma, all other causes are referred to as Cushing's syndrome
ACTH dependent
Pituitary adenoma (68%) → Cushing's disease
Ectopic ACTH (12%) - carcinoid/carcinoma e.g. lung, pancreas
Ectopic CRH (<1%)
ACTH independent
(Exogenous steroids)
Adrenal adenoma (10%) or carcinoma (8%)
Adrenal cortical nodular hyperplasia (1%)
False positive (pseudo) - severe depression, severe alcoholism
Pathophysiology
ACTH-independent
Autonomous over-production of cortisol by the adrenal gland due to neoplasia/nodular hyperplasia
Adrenal enlargement in ACTH-independent disease is usually nodular
ACTH-dependent
Adrenal enlargement in ACTH-dependent disease is usually diffuse