Examkin

Question

Difficulty: MediumDiagnostic Workup and Test Sequencing

A 48-year-old man presents to the primary care clinic reporting worsening fatigue, excessive sweating, and joint pain in his knees and hands over the past year. He mentions that his wedding ring no longer fits and he recently had to purchase shoes two sizes larger than his usual size. He has a history of newly diagnosed hypertension and obstructive sleep apnea. Vital signs show a blood pressure of 152/94 mm Hg, heart rate of 76/min, and respiratory rate of 14/min. Physical examination reveals coarse facial features, a prominent mandible, macroglossia, and enlarged, doughy hands. Visual field testing by confrontation is normal. A serum insulin-like growth factor-1 (IGF-1) level is ordered and returns markedly elevated for his age and sex. Which of the following is the most appropriate next step in the patient's diagnostic workup?

  1. Measurement of serum growth hormone following an oral glucose loadAnswer
  2. B
    Magnetic resonance imaging of the pituitary gland
  3. C
    Measurement of a single random serum growth hormone level
  4. D
    Measurement of serum growth hormone-releasing hormone level
  5. E
    Referral for transsphenoidal surgical resection

Answer

Measurement of serum growth hormone following an oral glucose load
In the diagnostic workup of acromegaly, an elevated IGF-1 is a highly sensitive initial screening test, but the diagnosis must be definitively confirmed with an oral glucose tolerance test (OGTT). In healthy individuals, a glucose load suppresses growth hormone (GH) secretion to very low levels. In patients with acromegaly, autonomous secretion from a pituitary adenoma causes GH levels to remain elevated despite the glucose load. This biochemical confirmation is absolutely required before proceeding to structural imaging studies.

Step-by-Step Solution

1
Analyze the patient's clinical presentation.
The patient exhibits classic symptoms of acromegaly, including enlarging extremities, coarse facial features, macroglossia, and associated conditions like hypertension and sleep apnea.
Establishing the pre-test probability directs the appropriate diagnostic pathway.
2
Evaluate the results of the initial investigation.
The serum IGF-1 level is markedly elevated, which serves as a positive initial screening test for acromegaly.
IGF-1 provides an integrated measure of growth hormone secretion over time, making it the best initial screening test.
3
Determine the proper sequence of the diagnostic workup.
The correct algorithm for acromegaly is: Clinical suspicion → Screen (IGF-1) → Confirm (oral glucose tolerance test with GH measurement) → Localize (MRI pituitary).
Following evidence-based guidelines prevents unnecessary invasive testing, misdiagnosis from incidentalomas, and inappropriate treatments.
4
Select the next indicated step based on the algorithm.
Since the screening test (IGF-1) is positive, the next required step is the confirmatory oral glucose tolerance test.
Biochemical confirmation must be obtained before imaging the pituitary gland.

Key Concept

The diagnostic workup for acromegaly requires sequential testing: initial screening with serum IGF-1, followed by biochemical confirmation using an oral glucose tolerance test (OGTT) to demonstrate a failure of growth hormone suppression, and finally, MRI of the pituitary gland for tumor localization.
Rate this question

Topics

Diagnostic Workup and Test Sequencing

More questions from this topic