What is the most common cause of Cushing disease?

Cushing disease specifically refers to the condition caused by excessive secretion of adrenocorticotropic hormone (ACTH) from a pituitary adenoma, which leads to increased production of cortisol from the adrenal glands. This is distinct from Cushing syndrome, which can be caused by various factors, including adrenal tumors or exogenous sources like steroid use.

The most frequent cause of Cushing disease, therefore, is indeed a pituitary adenoma. This type of tumor is typically benign and is characterized by hypersecretion of ACTH, stimulating the adrenal glands and resulting in elevated cortisol levels, which leads to the symptoms associated with Cushing disease.

While adrenal tumors and nonpituitary tumors that produce ACTH can lead to Cushing syndrome, they do not specifically define Cushing disease, which is exclusively linked to a pituitary origin. Additionally, prednisone use, although it can cause a steroid-induced form of Cushing syndrome, does not contribute to Cushing disease itself, as it involves exogenous hormone administration rather than endogenous overproduction due to a pituitary source.

Thus, when considering the specific context of Cushing disease, the pituitary adenoma is the most recognized and prevalent cause.