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Difficulty: EasyEndocrinology and Metabolism

A 35-year-old woman presents to the clinic with progressive weight gain, proximal muscle weakness, and easy bruising over the past eight months. Physical examination reveals central obesity, facial plethora, and wide, violaceous striae on her abdomen. The physician suspects Cushing syndrome. Arrange the following diagnostic steps in the correct chronological sequence to accurately establish the diagnosis and localize the etiology.

  1. 1Confirm the presence of pathological hypercortisolism using a 24-hour urine free cortisol, late-night salivary cortisol, or low-dose dexamethasone suppression test.
  2. 2Measure the plasma adrenocorticotropic hormone (ACTH) level to determine if the hypercortisolism is ACTH-dependent or ACTH-independent.
  3. 3Perform a high-dose dexamethasone suppression test or CRH stimulation test to differentiate between pituitary and ectopic sources of ACTH.
  4. 4Obtain targeted anatomical imaging, such as magnetic resonance imaging (MRI) of the pituitary gland or computed tomography (CT) of the adrenal glands, to localize the lesion.

Answer

The correct sequence is: confirm hypercortisolism, measure ACTH levels, perform high-dose dexamethasone testing (if ACTH-dependent), and finally obtain targeted imaging.
The diagnostic workup for Cushing syndrome relies on a strict progression from biochemical confirmation to anatomical localization. The physician must first confirm endogenous hypercortisolism. Second, ACTH is measured to categorize the disease as ACTH-dependent or independent. Third, high-dose suppression testing differentiates pituitary from ectopic sources. Finally, targeted imaging is ordered based on the biochemical evidence to avoid the trap of anatomical incidentalomas.

Step-by-Step Solution

1
Confirm hypercortisolism
Establishes the biochemical diagnosis of Cushing syndrome.
Prevents extensive workup in patients with normal cortisol physiology or pseudo-Cushing states.
2
Measure plasma ACTH
Differentiates ACTH-independent (adrenal) from ACTH-dependent (pituitary or ectopic) hypercortisolism.
Guides the subsequent biochemical tests and determines which organ system is driving the excess cortisol.
3
Perform high-dose dexamethasone suppression
Differentiates pituitary Cushing disease from ectopic ACTH secretion.
Pituitary adenomas retain some negative feedback mechanisms and will suppress cortisol production at high doses, whereas ectopic tumors (e.g., small cell lung cancer) will not.
4
Obtain targeted imaging
Anatomically localizes the biochemically proven tumor.
Imaging must be delayed until this step because benign, non-functioning incidentalomas of the pituitary and adrenal glands are common in the general population.

Key Concept

Diagnostic algorithm for Cushing syndrome
Estimated Time:1m 0s
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Topics

Endocrinology and Metabolism

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