Cushing Syndrome and Adrenal Insufficiency

Cushing syndrome and primary adrenal insufficiency sit at opposite ends of cortisol physiology. Cushing syndrome reflects chronic cortisol excess. Primary adrenal insufficiency, often called Addison disease, results from destruction of the adrenal cortex and inadequate production of cortisol and aldosterone. Cortisol helps maintain vascular tone, supports the stress response, and regulates glucose availability. Too much cortisol drives protein breakdown, insulin resistance, fat redistribution, hypertension, immune suppression, and bone loss. Too little cortisol leaves the body unable to maintain blood pressure, glucose availability, and an adequate response to illness or injury. Aldosterone is the major distinction between primary and central adrenal insufficiency. In primary disease, the damaged adrenal cortex cannot produce enough aldosterone. Sodium is lost, potassium is retained, and circulating volume falls. In central adrenal insufficiency caused by inadequate pituitary ACTH, aldosterone production is usually preserved because it is regulated mainly by the renin-angiotensin-aldosterone system. Cushing syndrome is also classified by the source of cortisol excess: - ACTH-dependent Cushing syndrome results from excessive ACTH stimulation, most commonly a pituitary adenoma, called Cushing disease, or an ectopic ACTH-secreting tumor. - ACTH-independent...