Acromegaly with initial negative oral glucose tolerance test: a case report

Area of Science:

• Endocrinology
• Neurosurgery
• Oncology

Background:

• Acromegaly diagnosis typically relies on growth hormone (GH) levels ≥ 1 µg/L post-oral glucose tolerance test (OGTT).
• However, normal GH suppression during OGTT may not definitively exclude acromegaly.
• Pituitary adenomas can present incidentally or with subtle symptoms.

Observation:

• A 55-year-old man with an incidentally discovered pituitary macroadenoma had elevated insulin-like growth factor-1 (IGF-1) despite GH < 1 µg/L post-OGTT.
• Initial suspicion of fracture-related IGF-1 elevation was considered, but IGF-1 remained high.
• Dizziness and recurrent IGF-1 elevation occurred a year later, alongside secondary hypocortisolism.

Findings:

• Follow-up OGTT revealed GH > 1 µg/L, confirming acromegaly.
• Endoscopic endonasal surgery successfully resected the pituitary macroadenoma.
• Post-surgery, pathology confirmed GH and prolactin staining, and IGF-1 normalized.

Implications:

• Normal GH suppression post-OGTT cannot exclude acromegaly, especially in pituitary adenoma patients.
• Mild or absent clinical acromegaly symptoms can occur.
• Close monitoring for acromegaly and hypopituitarism is crucial for patients with pituitary adenomas and elevated IGF-1.