Cushing's Disease (pituitary adenoma)

The dexamethasone suppression testing results (repeated below) show a failure of suppression at the low dose (cortisol remains above 3), but the cortisol level does suppress to greater than 50% if its initial value after the high dose. This finding is characteristic of hypercortisolism due to an ACTH-producing adrenal adenoma (Cushing's Disease).

             Patient        Reference
Baseline    11.9  mg/d      3.0 - 8.0
Low dose      8.0 mg/d          <3
High dose     3.1 mg/d         >50% suppression w/ pit. dis.

In this case, a CT scan of the head revealed a pituitary microadenoma, which was subsequently removed by trans-sphenoidal resection. Immunohistochemistry using anti-ACTH antibodies against a tissue section from the pituitary tumor confirmed ACTH production within the adenoma.