The clinical manifestation of pathological hypercortisolism from any cause.
Cushing's disease, which is hypercortisolism caused by an adrenocorticotropic hormone (ACTH)-secreting pituitary adenoma, is the most common cause of Cushing's syndrome, and is responsible for 70% to 80% of cases.
Though uncommon, the prevalence of endogenous Cushing's syndrome is greater than previously thought.
It may be difficult to distinguish patients with mild Cushing's syndrome from those with the metabolic syndrome (central obesity with insulin resistance, and hypertension). Features more specific to Cushing's syndrome include proximal muscle weakness, supraclavicular fat pads, facial plethora, violaceous striae, easy bruising, and premature osteoporosis.
After exclusion of exogenous corticosteroid use, patients with suspected Cushing's syndrome should be tested for hypercortisolism with 1 of 4 high-sensitivity tests (late-night salivary cortisol; 1 mg overnight low-dose dexamethasone suppression testing, 24-hour urinary free cortisol; or 48-hour 2 mg dexamethasone suppression testing).
At least 1 additional test should be used to confirm hypercortisolism in patients with a positive initial screening test.
Once endogenous hypercortisolism is confirmed, plasma ACTH should be measured. If ACTH is suppressed, diagnostic testing should focus on the adrenal glands. If ACTH is not suppressed, pituitary or ectopic disease should be sought.
In the vast majority of cases of endogenous Cushing's syndrome, surgical resection of the pituitary adenoma or adrenal adenoma that is causing hypercortisolism is the primary treatment of choice.
Cushing's syndrome is the clinical manifestation of pathological hypercortisolism from any cause. Patients often display weight gain with central obesity, facial rounding and plethora, proximal muscle weakness, and thinning of the skin. They also develop metabolic complications including diabetes mellitus, dyslipidaemia, metabolic bone disease, and hypertension. Cushing's syndrome can be caused by adrenocorticotropic hormone (ACTH)-secreting pituitary tumours (termed Cushing's disease), by autonomous adrenal cortisol overproduction, and, rarely, by ectopic ACTH-secreting tumours. 
Professor of Medicine (Endocrinology) and Neurological Surgery
Oregon Health & Science University
MF is an author of several references cited in this monograph. She is a scientific consultant and principal investigator (with a grant to the university) for Novartis and Strongbridge. She is an unpaid medical advisor for the Cushing's Support and Research Foundation; she is also chair of the Endocrine Society Guidelines Committee, chair of the Pituitary Society Physician Education Committee, and member of the Board of Directors of the Pituitary Society.
Professor of Medicine
Director of Research
College of Medical and Dental Sciences
University of Birmingham
Honorary Consultant Physician
Queen Elizabeth Hospital
PMS declares that he has no competing interests.
Department of Endocrinology
University Hospital of Bordeaux
AT declares that he has no competing interests.
Endocrine Research Department
Instituto de Investigaciones Médicas A. Lanari
University of Buenos Aires and IDIM-CONICET
LC declares that she has no competing interests.
Professor of Medicine
Division of Endocrinology, Diabetes & Metabolism
University of Texas Medical School
PRO declares that he has no competing interests.
Department of Endocrine Neoplasia and Hormonal Disorders
Division of Internal Medicine
University of Texas MD Anderson Cancer Center
MAH declares that he has no competing interests.
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