What would indicate a positive result for Cushing's disease in a low-dose dexamethasone suppression test?

In the context of a low-dose dexamethasone suppression test, a positive result for Cushing's disease is characterized by no suppression of cortisol levels following the administration of the dexamethasone. In healthy individuals, dexamethasone, a synthetic glucocorticoid, usually suppresses cortisol production due to its negative feedback mechanism on the hypothalamic-pituitary-adrenal (HPA) axis. However, in Cushing's disease, which is commonly caused by an adrenal adenoma or pituitary adenoma producing excessive ACTH, this feedback mechanism is disrupted.

When there is no suppression of cortisol after the administration of low-dose dexamethasone, it indicates that the body's regulatory mechanisms are unable to reduce cortisol levels, confirming the presence of hypercortisolism typical of Cushing's disease. Increased salivary cortisol levels would suggest abnormal cortisol production but do not directly indicate a positive suppression test; suppression of cortisol is expected in healthy individuals, making it the opposite of what is seen in Cushing's disease. Decreased ACTH levels are often associated with adrenal causes of hypercortisolism rather than pituitary causes. Thus, the correct interpretation of the test in the context of Cushing