Cushing syndrome
Formal Definition
A clinical syndrome resulting from chronic exposure to excess glucocorticoids, either from exogenous sources (exogenous Cushing syndrome) such as corticosteroid medications, or from endogenous overproduction (endogenous Cushing syndrome) via ACTH-secreting pituitary adenoms (Cushing disease, ~70% of endogenous cases), adrenal tumors, or ectopic ACTH secretion from small cell lung cancer, carcinoid tumors, or pancreatic neuroendocrine tumors.
How It's Used on the Ward
"Cushinging" or "cushings" — the constellation of central obesity, moon facies, purple striae, and proximal myopathy from too much cortisol; the moon face and buffalo hump are the visual giveaways on rounds.
Example
""28-year-old female with 15 kg weight gain over 2 years, new hypertension and irregular periods, easy bruising. 24h urinary cortisol elevated at 380 μg (normal <100). 1mg overnight dexamethasone suppression test: cortisol 18 μg/dL (failed to suppress). Pituitary MRI shows 8mm adenoma. Diagnosis: Cushing disease — pituitary ACTH adenoma causing endogenous hypercortisolism.""
Clinical Context
Differential of hypercortisolism: ACTH-dependent (pituitary Cushing disease, ectopic ACTH from肺癌/pancreatic NET) vs ACTH-independent (adrenal adenoma, adrenal carcinoma, exogenous steroids). Diagnostic tests: 24h urinary free cortisol (3x upper limit = positive), late-night salivary cortisol, 1mg overnight dexamethasone suppression test (cortisol >1.8 μg/dL = failure to suppress), ACTH level (high = ACTH-dependent, low = ACTH-independent). Pituitary source: inferior petrosal sinus sampling (IPSS) with CRH stimulation. Adrenal source: CT abdomen. Treatment: transsphenoidal surgery for pituitary adenoma, adrenalectomy for adrenal tumors, ketoconazole or metyrapone for medical management. Classic signs: central obesity, moon facies, buffalo hump, supraclavicular fat pads, purple striae (>1cm), proximal muscle weakness, easy bruising, proximal myopathy, psychiatric changes. Pseudo-Cushing: severe obesity, depression, alcoholism — can mimic Cushing labs.