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Zorluk: OrtaEndocrinology and Metabolism

A 42-year-old woman presents to the clinic with progressive weight gain, easy bruising, and proximal muscle weakness over the past 8 months. Physical examination reveals facial plethora, prominent supraclavicular fat pads, and purple abdominal striae. Her blood pressure is 155/95 mmHg. The physician suspects Cushing syndrome and plans to initiate a diagnostic workup. Arrange the following diagnostic steps in the correct chronological sequence, from the initial action to the final localizing step.

  1. 1Review medication history to exclude exogenous glucocorticoid exposure
  2. 2Perform initial biochemical screening (e.g., 24-hour urine free cortisol or late-night salivary cortisol)
  3. 3Measure early morning plasma adrenocorticotropic hormone (ACTH) levels
  4. 4Perform a high-dose dexamethasone suppression test or pituitary magnetic resonance imaging (MRI)

Cevap

The correct chronological sequence for diagnosing Cushing syndrome is to first exclude exogenous glucocorticoid exposure, followed by confirming endogenous hypercortisolism with initial screening tests, then measuring plasma ACTH to determine ACTH dependence, and finally performing a high-dose dexamethasone suppression test or pituitary MRI to localize the ACTH source.
The diagnostic evaluation of Cushing syndrome follows a strict stepwise approach to prevent diagnostic errors and unnecessary procedures. Exogenous glucocorticoid use is the most common etiology and must be ruled out clinically. Next, endogenous hypercortisolism is established using highly sensitive screening tests (e.g., 24-hour urine free cortisol, late-night salivary cortisol, or low-dose dexamethasone suppression test). Only after hypercortisolism is biochemically confirmed should early morning plasma ACTH be measured to classify the condition as ACTH-dependent or ACTH-independent. Finally, if the condition is ACTH-dependent, specialized testing (such as a high-dose dexamethasone suppression test, CRH stimulation test, or pituitary MRI) is utilized to differentiate a pituitary source (Cushing disease) from an ectopic source.

Adım Adım Çözüm

1
Exclude exogenous glucocorticoid exposure.
Rules out iatrogenic Cushing syndrome.
Exogenous glucocorticoids are the most common cause of Cushingoid features and require no further biochemical evaluation if identified.
2
Perform initial biochemical screening (e.g., 24-hour urine free cortisol).
Confirms the presence of endogenous hypercortisolism.
Pathological hypercortisolism must be definitively proven before investigating its specific source to avoid false-positive diagnostic cascades.
3
Measure early morning plasma ACTH.
Categorizes the syndrome as ACTH-dependent or ACTH-independent.
A suppressed ACTH level points to an adrenal tumor, whereas a normal or elevated ACTH level points to a pituitary or ectopic source.
4
Perform high-dose dexamethasone suppression test or pituitary MRI.
Localizes the ACTH-dependent source.
This is necessary to differentiate a pituitary adenoma (Cushing disease), which typically suppresses with high-dose dexamethasone, from ectopic ACTH secretion, which typically does not.

Anahtar Kavram

Diagnostic algorithm for Cushing syndrome
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Konular

Endocrinology and Metabolism

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