Patient A is suffering from ACTH hyper secretion, which occur as a result of excessive secretion of cortisol. That is why, the drug dexamethasone was able to effectively suppress the overproduction of the hormone. For the second patient, the patient is not suffering primarily from ACTH hyper secretion, that is why the production of ACTH remain high. The problem probably lies in the signalling pathway, which did not sense the presence of the suppressor drug.