This could be due to a pituitary adenoma secreting ACTH (Cushing's disease), or Cushing's syndrome from ectopic ACTH production, or idiopathic adrenal hyperplasia.

The way in which the pituitary gland regulates the normal production of steroid hormones by the adrenal gland is through the secretion of ACTH.

Dexamethasone, a synthetic glucocorticoid, is believed to bind to the glucocorticoid receptors located in the anterior pituitary, thereby reducing ACTH secretion, and ultimately cortisol production.