Match each patient scenario involving the evaluation of suspected or confirmed Cushing syn… — USMLE Step 3

Match each patient scenario involving the evaluation of suspected or confirmed Cushing syndrome with the most appropriate next step in their diagnostic workup.

A $42$ -year-old woman presents with recent central weight gain, violaceous striae, and proximal muscle weakness. No endocrinologic testing has been performed.Measurement of $24$ -hour urine free cortisol or $1$ -mg overnight dexamethasone suppression test
A $38$ -year-old man has confirmed hypercortisolism based on two abnormal screening tests. His morning plasma adrenocorticotropic hormone (ACTH) level is undetectable ( $< 5$ pg/mL).Computed tomography (CT) scan of the adrenal glands
A $45$ -year-old woman has confirmed hypercortisolism and an elevated morning plasma ACTH level ( $65$ pg/mL). Following an $8$ -mg high-dose dexamethasone suppression test, her serum cortisol level decreases by $80\%$ from baseline.Magnetic resonance imaging (MRI) of the pituitary gland
A $55$ -year-old man with a $30$ -pack-year smoking history has confirmed hypercortisolism and a markedly elevated plasma ACTH level ( $150$ pg/mL). A high-dose dexamethasone suppression test shows no significant reduction in serum cortisol levels.Computed tomography (CT) scan of the chest and abdomen

Cevap

The correct matches follow the established sequence: screen for hypercortisolism first (24-hour urine/low-dose dexamethasone), identify ACTH dependence for confirmed cases (Adrenal CT if suppressed ACTH), and use high-dose dexamethasone to differentiate ACTH-dependent sources (Pituitary MRI if suppressed, Chest/Abdomen CT if not suppressed).

The correct pairings align with standard endocrine guidelines for evaluating Cushing syndrome, which enforce a strict sequence: confirm excess cortisol production biochemically, measure ACTH to distinguish adrenal from central/ectopic sources, and use high-dose suppression testing to isolate ACTH-dependent pathologies before ordering any targeted imaging.

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Determine if hypercortisolism has been biochemically confirmed.

Patients without prior testing require initial screening with a 24-hour urine free cortisol, late-night salivary cortisol, or 1-mg dexamethasone suppression test.

Clinical signs alone are insufficient to diagnose Cushing syndrome, and premature anatomic imaging can detect clinically irrelevant incidentalomas.

Analyze the ACTH level in patients with confirmed hypercortisolism.

A suppressed ACTH level indicates an adrenal source (ACTH-independent), prompting an adrenal CT scan.

High cortisol levels normally suppress pituitary ACTH production; if ACTH is suppressed, the adrenal gland is autonomously producing cortisol.

Interpret the high-dose dexamethasone suppression test for patients with elevated ACTH.

Significant suppression (e.g., >50% reduction) points to a pituitary source, requiring a pituitary MRI. Lack of suppression points to an ectopic source, requiring a chest and abdominal CT.

Pituitary adenomas (Cushing disease) retain a partial negative feedback response to high-dose glucocorticoids, whereas ectopic ACTH-producing tumors typically do not respond to feedback.

Anahtar Kavram

Diagnostic algorithm for Cushing syndrome: Biochemical confirmation, followed by ACTH measurement, and targeted functional testing (high-dose dexamethasone) before appropriate anatomic imaging.

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