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

Which condition is a common cause of Cushing syndrome and is characterized by bilateral adrenal atrophy due to decreased ACTH?

1. Adrenal Cushing syndrome

2. Cushing disease

3. Ectopic Cushing syndrome

4. Exogenous Corticosteroids

The correct answer is: Exogenous Corticosteroids

The condition that commonly leads to Cushing syndrome and is characterized by bilateral adrenal atrophy due to decreased adrenocorticotropic hormone (ACTH) is the use of exogenous corticosteroids. When corticosteroids are administered externally (e.g., through medication like prednisone), they provide a negative feedback mechanism on the hypothalamus and pituitary gland. This feedback decreases the production of ACTH as the body perceives there to be adequate levels of glucocorticoids already circulating. As a result, the decreased ACTH levels cause the adrenal glands to receive less stimulation, leading to bilateral adrenal atrophy. Over time, the adrenal cortex becomes underdeveloped because it is not being regularly stimulated to produce cortisol, contributing to the hallmark symptoms of Cushing syndrome, which include weight gain, hypertension, and skin changes. In contrast, other conditions such as adrenal Cushing syndrome and Cushing disease arise from excess production of cortisol, leading to different pathological mechanisms and typically not involving bilateral adrenal atrophy due to low ACTH levels. Ectopic Cushing syndrome is caused by ectopic production of ACTH by non-pituitary tumors, which usually leads to increased adrenal stimulation rather than atrophy.