Cushing's syndrome
Also known as: hypercortisolism
Cushing's syndrome is the clinical condition caused by chronic exposure to excess cortisol. Hallmark features include central obesity, moon facies, a dorsal fat pad, purple striae, hypertension, and hyperglycemia.
Cushing's syndrome is the set of signs and symptoms produced by prolonged elevation of cortisol, the adrenal glucocorticoid hormone. Cortisol excess disrupts metabolism, immune function, bone, skin, and blood pressure regulation, producing a recognizable clinical picture regardless of the underlying source.
Causes divide into exogenous and endogenous. The most common cause overall is exogenous glucocorticoid therapy — long-term steroid treatment for conditions like asthma or autoimmune disease. Endogenous causes include an ACTH-secreting pituitary adenoma (called Cushing disease, the most common endogenous cause), cortisol-producing adrenal tumors, and ectopic ACTH secretion, classically from small cell lung cancer. Distinguishing these sources relies on ACTH levels and dexamethasone suppression testing: pituitary disease typically suppresses with high-dose dexamethasone, while ectopic ACTH and adrenal tumors do not respond the same way.
Clinical features reflect cortisol's actions: central obesity with thin extremities, a rounded "moon" face, a dorsocervical fat pad, wide purple abdominal striae, easy bruising, proximal muscle weakness, osteoporosis, hypertension, hyperglycemia, and increased infection risk. Patients may also develop mood changes and, in women, irregular menses and hirsutism.
Cushing's syndrome is a high-yield endocrine topic on the USMLE Step 1 exam, which emphasizes the causes and diagnostic workup, and it also appears on the NPTE-PT and NPTE-PTA exams, where physical therapy candidates must recognize its musculoskeletal effects such as proximal weakness and osteoporosis.
Key takeaways
- Cushing's syndrome results from chronic cortisol excess, most commonly from exogenous steroid therapy.
- Cushing disease specifically means an ACTH-secreting pituitary adenoma, the most common endogenous cause.
- Classic features include central obesity, moon facies, purple striae, hypertension, hyperglycemia, and proximal weakness.
- ACTH levels and dexamethasone suppression testing distinguish pituitary, adrenal, and ectopic sources.
- USMLE Step 1 tests the diagnostic workup, while the NPTE exams focus on recognizing its clinical presentation.