Importance: Cushing syndrome is defined as a prolonged increase in plasma cortisol levels that is not due to a physiological etiology. Although the most frequent cause of Cushing syndrome is exogenous steroid use, the estimated incidence of Cushing syndrome due to endogenous overproduction of cortisol ranges from 2 to 8 per million people annually. Cushing syndrome is associated with hyperglycemia, protein catabolism, immunosuppression, hypertension, weight gain, neurocognitive changes, and mood disorders.
Observations: Cushing syndrome characteristically presents with skin changes such as facial plethora, easy bruising, and purple striae and with metabolic manifestations such as hyperglycemia, hypertension, and excess fat deposition in the face, back of the neck, and visceral organs. Cushing disease, in which corticotropin excess is produced by a benign pituitary tumor, occurs in approximately 60% to 70% of patients with Cushing syndrome due to endogenous cortisol production. Evaluation of patients with possible Cushing syndrome begins with ruling out exogenous steroid use. Screening for elevated cortisol is performed with a 24-hour urinary free cortisol test or late-night salivary cortisol test or by evaluating whether cortisol is suppressed the morning after an evening dexamethasone dose. Plasma corticotropin levels can help distinguish between adrenal causes of hypercortisolism (suppressed corticotropin) and corticotropin-dependent forms of hypercortisolism (midnormal to elevated corticotropin levels). Pituitary magnetic resonance imaging, bilateral inferior petrosal sinus sampling, and adrenal or whole-body imaging can help identify tumor sources of hypercortisolism. Management of Cushing syndrome begins with surgery to remove the source of excess endogenous cortisol production followed by medication that includes adrenal steroidogenesis inhibitors, pituitary-targeted drugs, or glucocorticoid receptor blockers. For patients not responsive to surgery and medication, radiation therapy and bilateral adrenalectomy may be appropriate.
Conclusions and relevance: The incidence of Cushing syndrome due to endogenous overproduction of cortisol is 2 to 8 people per million annually. First-line therapy for Cushing syndrome due to endogenous overproduction of cortisol is surgery to remove the causative tumor. Many patients will require additional treatment with medications, radiation, or bilateral adrenalectomy.