A 48-year-old man comes to the primary care clinic reporting progressive fatigue, excessive sweating, and generalized joint pain, particularly in his knees and hands, over the past two years. The patient mentions that his wedding ring no longer fits and he recently had to purchase larger shoes. His medical history is unremarkable, and he takes no medications. Vital signs show a blood pressure of 155/95 mmHg, a heart rate of 76/min, a respiratory rate of 14/min, and a BMI of 29 kg/m^2. Physical examination reveals a prominent jaw, widely spaced teeth, coarse facial features, and enlarged, doughy hands. Which of the following is the most appropriate next step in laboratory evaluation?
- Measurement of serum insulin-like growth factor-1 concentrationAnswer
- BRandom measurement of serum growth hormone concentration
- COral glucose tolerance test with concurrent growth hormone measurement
- DMagnetic resonance imaging of the pituitary gland
- EMeasurement of serum thyroid-stimulating hormone concentration
Answer
Measurement of serum insulin-like growth factor-1 concentration
The correct answer is the measurement of serum insulin-like growth factor-1 (IGF-1) concentration. This patient presents with classic signs and symptoms of acromegaly, a syndrome typically caused by a growth hormone (GH)-secreting pituitary adenoma. The initial diagnostic step for suspected acromegaly is measuring the serum IGF-1 level. Because GH is secreted in a highly pulsatile manner and has a short circulating half-life, a single random GH measurement is unreliable. In contrast, IGF-1 is produced primarily by the liver in response to GH, has a long half-life, and provides a stable, integrated assessment of GH secretion over time. If the IGF-1 level is elevated, the diagnosis is subsequently confirmed with an oral glucose tolerance test.
Step-by-Step Solution
Key Concept
Initial biochemical screening for acromegaly
Estimated Time:1m 15s