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Difficulty: MediumDiagnostic Workup and Test Sequencing

A 42-year-old female presents to the outpatient clinic reporting progressive joint pain, increased sweating, and noticing that her shoe size has increased over the past two years. She also mentions having to resize her wedding ring twice recently due to her fingers becoming "too thick." Her past medical history is significant for newly diagnosed hypertension and type 2 diabetes mellitus, which are currently managed with amlodipine and metformin. Vital signs include a blood pressure of 148/92 mmHg, a heart rate of 78/min, and a BMI of 29 kg/m^2. Physical examination reveals a prominent jaw, a visibly enlarged tongue, and coarse facial features. Her hands are notably fleshy with broadened fingers. Which of the following is the most appropriate initial step in the diagnostic workup?

  1. Measurement of serum insulin-like growth factor 1 levelAnswer
  2. B
    Measurement of a random serum growth hormone level
  3. C
    Oral glucose suppression test with growth hormone measurement
  4. D
    Magnetic resonance imaging of the pituitary gland
  5. E
    Measurement of serum thyroid-stimulating hormone and free thyroxine

Answer

Measurement of serum insulin-like growth factor 1 level
The correct initial diagnostic step for a patient presenting with classic signs of acromegaly (acral overgrowth, coarse facial features, and metabolic derangements) is the measurement of insulin-like growth factor 1 (IGF-1). Because growth hormone is secreted in a pulsatile manner, a single random measurement is unreliable. IGF-1 provides a stable, integrated measure of growth hormone secretion over time, making it the most sensitive initial screening test.

Step-by-Step Solution

1
Identify the underlying clinical syndrome based on the patient's presentation.
The combination of acral overgrowth (increasing shoe and ring size), coarse facial features, macroglossia, hyperhidrosis, and newly diagnosed metabolic conditions (hypertension, diabetes mellitus) strongly points to a diagnosis of acromegaly.
Recognizing the constellation of symptoms is essential before initiating the diagnostic pathway.
2
Recall the diagnostic algorithm and proper test sequencing for suspected acromegaly.
The correct sequence is: biochemical screening, followed by biochemical confirmation, and finally anatomical localization.
Adhering to evidence-based sequencing avoids false positives from premature imaging and incorrect interpretations from volatile biomarkers.
3
Select the appropriate initial screening test for the sequence.
Insulin-like growth factor 1 (IGF-1) is the correct choice, as its stable serum concentration directly correlates with overall growth hormone activity.
Direct growth hormone measurement is unreliable due to pulsatile secretion, making IGF-1 the most accurate and cost-effective initial step.

Key Concept

The diagnostic workup for suspected acromegaly begins with a screening serum insulin-like growth factor 1 (IGF-1) level, followed by a confirmatory oral glucose suppression test if the IGF-1 is elevated, and concluding with a pituitary MRI for anatomical localization.
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Diagnostic Workup and Test Sequencing

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