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

Which type of Cushing syndrome is predominantly caused by primary adrenal adenomas, hyperplasia, or carcinomas leading to decreased ACTH levels?

1. Adrenal Cushing syndrome

2. Cushing disease

3. Ectopic Cushing syndrome

4. Exogenous Corticosteroids

The correct answer is: Adrenal Cushing syndrome

The correct answer is the type of Cushing syndrome predominantly caused by primary adrenal adenomas, hyperplasia, or carcinomas leading to decreased ACTH levels, known as Adrenal Cushing syndrome. In this condition, the adrenal gland itself is producing excessive cortisol independently of ACTH regulation due to either an adrenal tumor or hyperplasia. As a result, the high levels of cortisol provide negative feedback to the pituitary gland, leading to decreased secretion of ACTH (adrenocorticotropic hormone). Cushing disease, on the other hand, specifically refers to a pituitary adenoma that secretes excess ACTH, resulting in increased cortisol production from the adrenal glands, and thus is characterized by elevated ACTH levels. Ectopic Cushing syndrome involves tumors located outside the pituitary that secrete ACTH, leading to a similar increase in cortisol levels; however, these conditions do not originate from adrenal abnormalities. Exogenous corticosteroids are not related to endogenous overproduction of cortisol but rather are caused by external administration of corticosteroids, leading to iatrogenic Cushing syndrome. Therefore, Adrenal Cushing syndrome is characterized by decreased ACTH levels due to the dysfunctional adrenal tissue producing cortisol autonomously.