Cushing's syndrome describes the signs and symptoms associated with prolonged exposure to inappropriately high levels of the hormone cortisol. This can be caused by taking glucocorticoid drugs, or diseases that result in excess cortisol, adrenocorticotropic hormone (ACTH), or CRH levels.
Cushing's disease refers to a pituitary-dependent cause of Cushing's syndrome: a tumor (adenoma) in the pituitary gland produces large amounts of ACTH, causing the adrenal glands to produce elevated levels of cortisol. It is the most common non-iatrogenic cause of Cushing's syndrome, responsible for 70% of cases excluding glucocorticoid related cases. An easy way to distinguish Cushing's syndrome from Cushing's disease is that the measured ACTH levels are lower in the former. The decrease in ACTH is due to increased negative feedback of cortisol on the hypothalamus and anterior pituitary.
This pathology was described by Harvey Cushing in 1932. The syndrome is also called Itsenko-Cushing syndrome, hyperadrenocorticism or hypercorticism.
Cushing's syndrome is not confined to humans and is also a relatively common condition in domestic dogs and horses. It also occurs in cats, but rarely.

This video explains the complete workup of Cushing Syndrome, the causes, the diagnosis, and the full management. It is very thorough. I hope you enjoy