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Difficulty: MediumDiagnostic Workup and Test Sequencing

A 52-year-old man comes to the outpatient clinic for a routine follow-up. Over the past two years, he has noticed that his wedding ring no longer fits and he has had to purchase shoes two sizes larger than his previous size. He also reports new-onset frequent headaches, excessive daytime sweating, and bilateral knee pain. Six months ago, he was diagnosed with type 2 diabetes mellitus, which has been difficult to control despite maximum doses of metformin. His blood pressure is 158/96 mmHg, pulse is 76/min, and respirations are 14/min. Physical examination reveals coarse facial features, prominent supraorbital ridges, a large fleshy nose, and an enlarged tongue. His hands and feet are markedly enlarged with doughy skin. Which of the following is the most appropriate next step in the diagnostic evaluation of this patient?

  1. Serum insulin-like growth factor 1 levelAnswer
  2. B
    Serum growth hormone level following an oral glucose load
  3. C
    Random serum growth hormone level
  4. D
    Magnetic resonance imaging of the brain
  5. E
    Formal visual field perimetry

Answer

The most appropriate next step is to measure the serum insulin-like growth factor 1 (IGF-1) level.
The patient's clinical presentation of enlarged extremities, coarse facial features, headaches, sweating, and secondary diabetes mellitus is highly suspicious for acromegaly. The diagnostic workup for acromegaly strictly follows a stepwise approach. The most appropriate initial screening test is a serum insulin-like growth factor 1 (IGF-1) level. Because growth hormone is secreted in a pulsatile fashion with a short half-life, random growth hormone levels are unreliable. IGF-1, however, is synthesized by the liver in response to growth hormone and has a much longer half-life, providing a stable reflection of average growth hormone levels over time.

Step-by-Step Solution

1
Analyze the clinical presentation.
The patient presents with enlarging extremities (ring and shoe size), coarse facial features, hyperhidrosis, arthropathy, and new-onset, difficult-to-control diabetes and hypertension.
These findings are classic for acromegaly, a syndrome typically caused by a growth hormone-secreting pituitary adenoma.
2
Determine the proper diagnostic testing sequence for suspected acromegaly.
The first step is biochemical screening, followed by biochemical confirmation, and finally structural localization.
Standard endocrinology guidelines require demonstrating biochemical hormone excess before pursuing anatomical imaging to avoid the confusion of incidentalomas.
3
Identify the specific initial screening test.
Serum IGF-1 level is the best initial test.
Growth hormone levels fluctuate widely throughout the day due to pulsatile secretion, making a random level useless. IGF-1 levels remain stable and reflect integrated growth hormone exposure.

Key Concept

The initial step in evaluating suspected acromegaly is screening with a serum insulin-like growth factor 1 (IGF-1) level, followed by confirmatory testing with an oral glucose suppression test if the IGF-1 is elevated.
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Diagnostic Workup and Test Sequencing

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