Cushing syndrome, Addison disease, pituitary adenomas, and ADH disorders (SIADH and diabetes insipidus) with their hallmark lab findings.
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- What is Cushing syndrome caused by?
- Chronic exposure to excess cortisol
- What is the most common overall cause of Cushing syndrome?
- Exogenous glucocorticoid use (e.g., prednisone therapy)
- What is the most common cause of endogenous Cushing syndrome?
- An ACTH-secreting pituitary adenoma (Cushing disease)
- What is the classic tumor causing ectopic ACTH secretion?
- Small cell lung carcinoma
- What is the purpose of the low-dose dexamethasone suppression test?
- To screen for Cushing syndrome (normally cortisol suppresses, but fails to in Cushing)
- In Cushing disease (pituitary source), does cortisol suppress with high-dose dexamethasone?
- Yes, it suppresses
- In ectopic ACTH-secreting tumors, does cortisol suppress with high-dose dexamethasone?
- No, it fails to suppress
- What skin finding is classic for Cushing syndrome?
- Purple (violaceous) abdominal striae
- What electrolyte abnormality is seen in Cushing syndrome, especially with ectopic ACTH?
- Hypokalemic metabolic alkalosis
- Why does Cushing syndrome cause hyperglycemia?
- Cortisol stimulates gluconeogenesis and antagonizes insulin
- What is a first-line screening test for Cushing syndrome?
- 24-hour urinary free cortisol
- What bone complication results from chronic Cushing syndrome?
- Osteoporosis (cortisol inhibits osteoblast activity)
- What is Addison disease?
- Primary adrenal insufficiency (the adrenal cortex itself fails)
- What is the most common cause of primary adrenal insufficiency in developed countries?
- Autoimmune adrenalitis
- What electrolyte finding is seen in Addison disease due to aldosterone deficiency?
- Hyperkalemia