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.
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