Which of the following statements about Cushing’s disease is true?

Cushing’s syndrome is due to increased adrenal cortisol production, regardless of etiology. Cushing’s disease usually is caused by a pituitary microadenoma producing high adrenocorticotropin (ACTH) levels. In most patients, cortisol levels would be suppressed as a result of the high-dose dexamethasone suppression test. Transsphenoidal microsurgical removal of the microadenoma is the treatment of choice in most centers.