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

Which type of Cushing syndrome is often associated with small cell carcinoma of the lung or other ectopic sources?

1. Adrenal Cushing syndrome

2. Cushing disease

3. Ectopic Cushing syndrome

4. Exogenous Corticosteroids

The correct answer is: Ectopic Cushing syndrome

Cushing syndrome often results from excessive levels of cortisol in the body, which can arise from different underlying causes. Ectopic Cushing syndrome specifically occurs when an ectopic source produces adrenocorticotropic hormone (ACTH), leading to excess cortisol production by the adrenal glands. This condition is frequently seen in patients with small cell carcinoma of the lung, among other tumors. The tumor cells release ACTH, which then stimulates the adrenal glands to secrete more cortisol. In contrast, adrenal Cushing syndrome originates from an adrenal source, typically due to an adrenal adenoma or carcinoma. Cushing disease refers to a pituitary adenoma that secretes ACTH, resulting in bilateral adrenal hyperplasia and excess cortisol. Exogenous corticosteroids are a result of outside administration of glucocorticoids, which can mimic Cushing syndrome but do not stem from the body’s own production of hormones. Thus, the key distinct feature of ectopic Cushing syndrome is the production of ACTH by non-pituitary tumors, such as small cell lung carcinoma, making it the correct choice for this question.