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?
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 coisol>50nmol/L at 8 am after 1mg dexamethasone tablet given at 11pm night before) Midnight plasma coisol levels>130ng/dl Midnight salivary coisol levels>5mmol/dl Low dose Dexamethasone test ( plasma coisol>50nmol/L after 0.5mg dexamethasone 6hourly for 2 days)
MRI to assess the adrenals
CT chest
Inferior petrosal sinus venous sampling
Coicotropin-releasing hormone (CRH) levels
Parathyroid and adrenal glands