What is a common cause of increased ACTH secretion in patients with Cushing's disease?

In Cushing's disease, increased adrenocorticotropic hormone (ACTH) secretion is most commonly caused by a pituitary adenoma that secretes excess ACTH. This situation leads to overstimulation of the adrenal glands, resulting in elevated cortisol levels and the characteristic features of Cushing's syndrome.

Chronic steroid exposure, which refers to the long-term administration of corticosteroids, can lead to secondary adrenal insufficiency and actually suppress ACTH production. On the other hand, dietary imbalance, genetic predisposition, and acute illness are not direct causes of elevated ACTH in this context. Instead, these factors might indirectly impact hormone levels or related conditions but do not lead to the primary increase in ACTH secretion as seen in Cushing’s disease. Thus, the presence of a pituitary adenoma is quintessential in the pathogenesis of excess ACTH in Cushing's disease, highlighting why chronic steroid exposure is pivotal in understanding the feedback mechanisms involved in hormone regulation.