HIGH ACTH LEVEL

HIGH ACTH LEVEL

 Q. A man with hypercortisolism is found to have an elevated ACTH level that suppresses

with high-dose dexmethasone. MRI of this pituitary shows no visible

lesion. What is the next best step in management?

a. Remove the pituitary

b. Repeat the dexamethasone suppression test

c. Use ketoconazole

d. Do petrosal venous sinus sampling

e. Order a PET scan of the brain

Answer: D.

MRI and CT of the brain lack both sensitivity and specificity in diagnosing

endocrine disorders. It is important to confirm the identity of an adrenal disorder

functionally prior to scanning the patient. This patient has high cortisol with a high

ACTH, indicating either the pituitary or an ectopic source of hyperadrenalism. The fact

that the ACTH levels suppress with high-dose dexamethasone indicates a pituitary

adenoma, which is the cause of Cushing syndrome in about 45 percent of patients. If

the tests point to a pituitary source but the scanning is indeterminant, inferior petrosal

sinus sampling is used to confirm it. Petrosal sinus sampling is also used to localize the

lesion, as well to see which half of a pituitary should be removed.