<prompt> Which of the following statements about Cushings disease is true?Serum adrenocoicotropin ACTH levels usually are lowPituitary microadenoma usually is presentThere is a high incidence of nonendocrine tumorsNonsuppression of coisol production by the high-dose dexamethasone suppression test is a characteristic finding  <response>: Cushings syndrome is due to increased adrenal coisol production, regardless of aetiology.Cushings disease usually is caused by a pituitary microadenoma producing high adrenocoicotropin ACTH levels.In most patients, coisol 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 centres. 