A 38-year-old woman is evaluated for progressive proximal muscle weakness, easy bruising, and irregular menses over the past 8 months. Physical examination shows central obesity, a dorsocervical fat pad, and wide purple striae on her abdomen. Blood pressure is 162/98 mm Hg. The physician suspects hypercortisolism and plans a stepwise diagnostic evaluation. Assume the results of each test necessitate further investigation to localize an occult source of adrenocorticotropic hormone (ACTH). Arrange the following diagnostic steps in the correct chronological sequence according to standard endocrine guidelines.
- 1Perform an overnight 1-mg low-dose dexamethasone suppression test
- 2Measure early morning plasma adrenocorticotropic hormone (ACTH) concentration
- 3Obtain a dedicated magnetic resonance imaging (MRI) scan of the pituitary gland
- 4Perform bilateral inferior petrosal sinus sampling (IPSS)
Answer
The correct sequence for evaluating Cushing syndrome is to first confirm hypercortisolism (low-dose dexamethasone suppression test), then determine ACTH dependence (plasma ACTH level), followed by initial localization (pituitary MRI), and finally invasive localization if imaging is inconclusive (inferior petrosal sinus sampling).
The algorithm for diagnosing Cushing syndrome requires a rigid stepwise approach to prevent diagnostic errors caused by physiological ACTH fluctuations and anatomical incidentalomas. The correct sequence is: biochemical confirmation of hypercortisolism, determination of ACTH dependence, non-invasive imaging, and finally invasive biochemical localization.
Step-by-Step Solution
Key Concept
The evaluation of Cushing syndrome follows a strict biochemical and radiographic sequence: 1) Confirm hypercortisolism, 2) Determine ACTH dependence, 3) Image the suspected source, 4) Perform invasive sampling if non-invasive tests are equivocal.