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Difficulty: MediumDiagnostic Workup and Test Sequencing

A 42-year-old man comes to the primary care clinic reporting a 9-month history of excessive sweating, fatigue, and bilateral knee pain. He also mentions that his wedding ring no longer fits and he recently had to purchase shoes that are a size larger than his previous footwear. His wife reports that his snoring has worsened significantly over the past year. Vital signs are within normal limits. Physical examination reveals a prominent supraorbital ridge, an enlarged tongue, and broad, doughy hands. Given the high clinical suspicion for a specific endocrine disorder, a serum insulin-like growth factor-1 (IGF-1) level is ordered and returns significantly elevated for his age and sex. Which of the following is the most appropriate next step in the diagnostic evaluation of this patient?

  1. Measurement of serum growth hormone following an oral glucose loadAnswer
  2. B
    Magnetic resonance imaging of the pituitary gland
  3. C
    Measurement of random serum growth hormone levels
  4. D
    Visual field testing by automated perimetry
  5. E
    Measurement of serum prolactin, adrenocorticotropic hormone, and thyroid-stimulating hormone

Answer

Measurement of serum growth hormone following an oral glucose load is the most appropriate next step to confirm the diagnosis.
The correct sequence for diagnosing acromegaly involves three distinct tiers. First, because growth hormone (GH) is secreted in a pulsatile fashion, the initial screening test is the measurement of serum insulin-like growth factor-1 (IGF-1), which provides a stable, integrated marker of GH activity over time. Since this patient's IGF-1 is elevated, the next required step is biochemical confirmation of autonomous GH secretion. The gold standard for this is the measurement of serum GH levels following an oral glucose load. In healthy individuals, glucose suppresses GH secretion; in patients with acromegaly, GH levels fail to suppress appropriately. Only after biochemical confirmation should imaging be pursued to localize the source.

Step-by-Step Solution

1
Analyze the clinical presentation
Identify classic signs of acromegaly: acral enlargement (ring size, shoe size), hyperhidrosis, macroglossia, and facial changes.
Recognizing the syndrome guides the initial screening strategy.
2
Evaluate the current position in the diagnostic sequence
The patient has already undergone the initial screening test (IGF-1), which is elevated.
Determining what has already been done prevents repetition and directs the next algorithmic step.
3
Determine the required confirmatory test
Select the oral glucose tolerance test (OGTT) to assess for lack of growth hormone suppression.
Before pursuing costly and potentially misleading structural imaging (MRI), functional biochemical autonomy must be confirmed.

Key Concept

The diagnostic sequence for acromegaly: initial screening with IGF-1, followed by biochemical confirmation with an oral glucose tolerance test, and finally localization with a pituitary MRI.
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Diagnostic Workup and Test Sequencing

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