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Question 14

A 28 yo nulligravid woman is referred for secondary amenorrhea. She has been gaining weight and has fatigue and muscle weakness. On exam, her BP is 165/95 and her weight is 99.8 kg. She has round facies, facial hirsutism, truncal obesity and has developed abdominal striae. What is the best screening test to confirm the diagnosis?

Answer Choices:

Overnight dexamethasone suppression test


Urinary 17-ketosteroids

Serum adrenocorticotropic hormone (ACTH)

Morning serum cortisol

Correct Answer:

Overnight dexamethasone suppression test


  • Cushing syndrome is overexposure of the body to cortisol. This is a rare diagnosis. It is different than Cushing disease (which implies a pituitary ACTH-secreting tumor)

  • Cushing syndrome can involve pituitary oversecretion or ectopic production of ACTH or corticotropin-releasing hormone. It can also occur due to an adrenal adenoma or carcinoma. Some people develop the condition because of exogenous corticosteroids

  • Diagnosis involves 2 steps:

  • Diagnosis and confirmation of hypersecretion of cortisol

  • Explore differential diagnosis and determine potential etiology

  • Those with Cushing syndrome exhibit oversecretion of cortisol that is not circadian in nature

  • Any of these screening tests can be performed: 24 hr urine cortisol, 1-mg overnight dexamethasone suppression test, serum or salivary midnight cortisol

  • Overnight dexamethasone suppression test is the simplest way of screening (give 1 mg of dexamethasone at 11 pm and measure plasma cortisol at 8 am).

  • A value of < 5 mg/dL rules out Cushing syndrome

  • After a positive overnight test, a high-dose dexamethasone suppression test is used to determine the etiology of Cushing syndrome