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Zorluk: ZorDiagnostic Workup and Test Sequencing

A 38-year-old female presents to the outpatient clinic with a chief complaint of rapid weight gain and easy bruising over the past year. She notes that her menstrual cycles have become irregular, occurring every 6 to 8 weeks. Her medical history includes well-controlled hypertension and polycystic ovary syndrome. Her current medications consist of lisinopril and a combined oral contraceptive pill. Vital signs include a temperature of 37.0°C (98.6°F), blood pressure of 154/96 mmHg, heart rate of 82/min, and respiratory rate of 14/min. Her body mass index is 34 kg/m 2^2. Physical examination demonstrates a plethoric face, prominent supraclavicular fat accumulation, and wide, purplish striae across the bilateral flanks and lower abdomen. She has trace pitting edema in the lower extremities and exhibits 4/5 strength in the proximal leg muscles. Fasting plasma glucose is 114 mg/dL. Due to strong clinical suspicion for hypercortisolism, a 1-mg overnight dexamethasone suppression test is performed. The 8:00 AM serum cortisol level the following morning is 12.4 μ\mu g/dL (normal: <1.8μ< 1.8 \mu g/dL).

Which of the following is the most appropriate next step in the diagnostic workup?

  1. Measurement of 24-hour urine free cortisolCevap
  2. B
    Measurement of plasma adrenocorticotropic hormone (ACTH) concentration
  3. C
    High-dose (8-mg) dexamethasone suppression test
  4. D
    Magnetic resonance imaging of the pituitary gland
  5. E
    Computed tomography of the abdomen and pelvis

Cevap

Measurement of 24-hour urine free cortisol
The correct answer is measurement of 24-hour urine free cortisol. This patient presents with classic features of Cushing syndrome and has an abnormal initial screening test (1-mg overnight dexamethasone suppression test). However, the diagnosis of Cushing syndrome requires at least two abnormal first-line screening tests before initiating the search for an etiology. Furthermore, this patient is taking an oral contraceptive pill containing estrogen, which increases the hepatic production of cortisol-binding globulin (CBG). Because the standard dexamethasone suppression test measures total serum cortisol, elevated CBG can cause a false-positive result. The most appropriate next step is to perform a second, distinct screening test that measures free (unbound) cortisol, such as a 24-hour urine free cortisol or late-night salivary cortisol. Only after hypercortisolism is unequivocally confirmed by two independent tests should plasma ACTH be measured.

Adım Adım Çözüm

1
Analyze the patient's clinical presentation and initial laboratory findings.
The patient exhibits classic signs of Cushing syndrome (weight gain, striae, proximal muscle weakness) and has an abnormal initial 1-mg overnight dexamethasone suppression test.
Establishing the preliminary diagnosis is necessary to navigate the correct diagnostic algorithm.
2
Evaluate the impact of the patient's current medications on diagnostic testing.
The patient is taking an oral contraceptive pill containing estrogen, which increases hepatic synthesis of cortisol-binding globulin (CBG).
Increased CBG leads to falsely elevated total serum cortisol, which can cause a false-positive result on the dexamethasone suppression test.
3
Determine the guideline-based next step for evaluating suspected hypercortisolism.
A second, distinct first-line screening test that measures free (unbound) cortisol, such as a 24-hour urine free cortisol or late-night salivary cortisol, must be performed.
Endocrine guidelines require two abnormal first-line tests to unequivocally establish the diagnosis of Cushing syndrome before checking ACTH levels or pursuing advanced imaging.

Anahtar Kavram

The diagnosis of Cushing syndrome requires biochemical confirmation with at least two abnormal first-line screening tests (e.g., 24-hour urine free cortisol, late-night salivary cortisol, or 1-mg overnight dexamethasone suppression test) prior to assessing etiology with plasma ACTH levels.
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Diagnostic Workup and Test Sequencing

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