<prompt> 36 year old female , asymptomatic but with raised 24-hour urinary coisol level and raised ACTH with suppression in high dose dexamethasone suppression test. MRI of head reveals no enlargement of the pituitary gland. What should be the next step in this case?MRI to assess the adrenalsCT chestInferior petrosal sinus venous samplingCoicotropin-releasing hormone CRH levels  <response>: This patient most likely has Cushing Syndrome because of positive screening test of 24-hr urinary coisol level. It is a secondary cause of Cushing Syndrome due to elevated ACTH levels. This may be either due to a pituitary adenoma or an ectopic source such as small cell lung cancer. MRI head would reveal any adenoma of pituitary gland but still if inconclusive it should be followed by sampling of inferior petrosal sinus Test for screening or confirmation of Cushing syndrome are: 24 hour urinary free coisol excretion Dexamethasone overnight test plasma coisol50nmolL at 8 am after 1mg dexamethasone tablet given at 11pm night before Midnight plasma coisol levels130ngdl Midnight salivary coisol levels5mmoldl Low dose Dexamethasone test plasma coisol50nmolL after 0.5mg dexamethasone 6hourly for 2 days 