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Difficulty: Very hardDiagnostic Workup and Test Sequencing

Match each patient presentation with the most appropriate next step in their diagnostic evaluation based on established sequential testing algorithms.

  • A 48-year-old man with refractory hypertension. Evaluation shows a plasma aldosterone-to-renin ratio of 42. Following an intravenous saline infusion test, aldosterone remains elevated. A high-resolution adrenal CT scan reveals structurally normal adrenal glands bilaterally.Bilateral adrenal venous sampling (AVS)
  • A 41-year-old woman with progressive weight gain and proximal muscle weakness. She has concordant elevations in 24-hour urine free cortisol and late-night salivary cortisol. Subsequent testing reveals a plasma ACTH level of 85 pg/mL (elevated).Magnetic resonance imaging (MRI) of the pituitary gland
  • A 34-year-old man with episodic headaches and resting tachycardia. Biochemical screening reveals plasma free normetanephrine levels six times the upper limit of normal. A contrast-enhanced CT of the abdomen and pelvis shows no adrenal or extra-adrenal masses.Functional imaging with 68-Ga-DOTATATE PET or 123-I-MIBG scintigraphy
  • A 28-year-old woman with a palpable anterior neck mass. Ultrasound reveals a 2.5-cm solid, hypoechoic thyroid nodule with irregular margins and microcalcifications. Her serum TSH level is 0.1 mU/L (suppressed).Radionuclide thyroid scintigraphy
  • A 55-year-old woman has a serum calcium of 11.2 mg/dL and an intact PTH of 120 pg/mL. Her 24-hour urinary calcium excretion is appropriately elevated. She meets established criteria for surgical intervention.Technetium-99m sestamibi scintigraphy and neck ultrasonography

Answer

The presentations map to their respective localizing and confirming studies: Refractory HTN/Normal CT -> AVS. High ACTH Cushing's -> Pituitary MRI. Occult Pheochromocytoma -> Functional PET/MIBG imaging. Nodule with Low TSH -> Radionuclide scintigraphy. Confirmed Hyperparathyroidism requiring surgery -> Sestamibi scan.
Diagnostic sequencing in endocrinology relies on three immutable phases: confirming biochemical excess, determining trophic hormone dependence, and finally localizing the source. Deviating from these sequences—such as skipping functional assessment before structural biopsy, or jumping to invasive sampling before initial non-invasive imaging—leads to premature interventions, misdiagnoses, or missed ectopic sources.

Step-by-Step Solution

1
Analyze the primary hyperaldosteronism scenario.
The patient has biochemically confirmed PA but a normal CT. AVS is the next indicated test.
CT scanning can miss microadenomas or reveal non-functioning incidentalomas. AVS definitively lateralizes aldosterone hypersecretion.
2
Analyze the Cushing syndrome scenario.
Hypercortisolism is confirmed, and ACTH is elevated, indicating ACTH-dependence.
A pituitary source (Cushing disease) is the most common cause of ACTH-dependent Cushing's, so a pituitary MRI is the first localization step.
3
Analyze the pheochromocytoma scenario.
Catecholamine excess is confirmed, but the standard abdominal/pelvic CT is negative.
Functional imaging (like DOTATATE PET or MIBG) scans the whole body to identify extra-adrenal paragangliomas.
4
Analyze the thyroid nodule scenario.
The ultrasound is highly suspicious, but the TSH is suppressed.
Guidelines mandate determining the functional status of a nodule with low TSH using scintigraphy before any biopsy, to prevent false-positive cytology from an autonomous adenoma.
5
Analyze the primary hyperparathyroidism scenario.
Diagnosis is fully confirmed (including 24h urine calcium) and surgical criteria are met.
Localization studies (sestamibi/ultrasound) are only indicated for surgical planning, not for diagnosis.

Key Concept

Applying strict sequential diagnostic algorithms in endocrine disorders to prevent unnecessary invasive procedures or surgical errors.
Estimated Time:2m 30s
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Topics

Diagnostic Workup and Test Sequencing

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