USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

The condition characterized by decreased ACTH and increased cortisol levels, often presenting as primary aldosteronism, corresponds to adrenal Cushing syndrome. This syndrome arises from an adrenal adenoma or carcinoma that autonomously produces cortisol, leading to hypercortisolism independent of ACTH regulation. In this scenario, the feedback mechanism inhibits ACTH secretion due to the elevated cortisol levels, resulting in low ACTH levels. This is distinct from other forms of Cushing syndrome, such as Cushing disease, where ACTH is elevated due to a pituitary adenoma, or ectopic Cushing syndrome, where ACTH is produced by non-pituitary tumors. Exogenous corticosteroids would also lead to low ACTH levels but do not typically present with the features of primary aldosteronism. Overall, the key features of adrenal Cushing syndrome are the high cortisol levels coupled with low ACTH, making it the underlying cause in this clinical context.