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Zorluk: ZorEndocrinology and Metabolism

A 39-year-old woman is evaluated for progressive weight gain, proximal muscle weakness, and new-onset facial hair growth over the past year. Physical examination reveals central adiposity, facial plethora, a dorsocervical fat pad, and wide violaceous abdominal striae. Her blood pressure is 158/96 mm Hg. Initial screening with two separate 24-hour urine free cortisol measurements and an overnight low-dose dexamethasone suppression test confirm the diagnosis of endogenous hypercortisolism.

Arrange the following diagnostic steps in the most appropriate chronological sequence to determine the specific etiology of her condition. Assume each test is performed sequentially and its result dictates the necessity of the immediate next step in this patient's diagnostic pathway.

  1. 1Measurement of plasma adrenocorticotropic hormone (ACTH) concentration
  2. 2Magnetic resonance imaging (MRI) of the pituitary gland
  3. 3Inferior petrosal sinus sampling (IPSS)
  4. 4Computed tomography (CT) scan of the chest and abdomen

Cevap

The correct diagnostic sequence is: 1) Plasma ACTH concentration, 2) MRI of the pituitary gland, 3) Inferior petrosal sinus sampling, 4) CT scan of the chest and abdomen.
The diagnostic algorithm for Cushing syndrome strictly requires establishing the biochemical source before proceeding to anatomical imaging. Once hypercortisolism is confirmed, plasma ACTH determines if the condition is ACTH-dependent. If ACTH is normal or elevated, a pituitary MRI is performed because pituitary adenomas are the most common cause. If the MRI is negative or equivocal (lesion < 6 mm), IPSS is mandatory to differentiate an occult pituitary microadenoma from an ectopic ACTH-secreting tumor. If IPSS confirms an ectopic source, whole-body imaging (such as CT of the chest and abdomen) is indicated to locate the primary tumor.

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1
Measurement of plasma ACTH concentration
Differentiates ACTH-dependent from ACTH-independent causes.
This biochemical step dictates the anatomical region to investigate. Suppressed ACTH directs attention to the adrenal glands, whereas normal/elevated ACTH points to a pituitary or ectopic source.
2
MRI of the pituitary gland
Assesses for a visible pituitary adenoma.
Since Cushing disease (a pituitary adenoma) accounts for the vast majority of ACTH-dependent cases, dedicated pituitary imaging is the appropriate next step.
3
Inferior petrosal sinus sampling (IPSS)
Definitively distinguishes between pituitary and ectopic ACTH secretion.
Because pituitary incidentalomas are common and true adenomas may be too small to visualize on MRI, IPSS is required when the MRI does not show a clear, definitive adenoma (> 6 mm).
4
CT scan of the chest and abdomen
Localizes an ectopic ACTH-secreting tumor.
Only after IPSS confirms an ectopic source (indicated by a lack of central-to-peripheral ACTH gradient) should extensive cross-sectional imaging be performed to locate tumors such as bronchial carcinoids or small cell lung cancer.

Anahtar Kavram

The diagnostic algorithm for Cushing syndrome progresses sequentially from confirming hypercortisolism to biochemical localization (ACTH), followed by anatomical localization via targeted imaging and, if necessary, venous sampling.
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Endocrinology and Metabolism

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