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

BACKGROUND: Acromegaly can be diagnosed by a growth hormone value ≥ 1 µg/L following an oral glucose tolerance test. However, normal growth hormone suppression following oral glucose tolerance test may not exclude acromegaly. CASE PRESENTATION: We present a case of a 55-year-old Chinese man with pituitary macroadenoma incidentally noted after a traffic accident. He reported feet enlargement in the past few years. At the beginning, elevated insulin-like growth factor-1 was noted with growth hormone value < 1 µg/L after oral glucose tolerance test. Fracture-related high insulin-like growth factor-1 was suspected. Insulin-like growth factor-1 decreased gradually but was still above the upper limit of normal . However, he suffered from dizziness 1 year later and insulin-like growth factor-1 increased again. Besides, secondary hypocortisolism developed. The size of the pituitary macroadenoma was stationary. Follow-up oral glucose tolerance test showed a growth hormone value > 1 µg/L. Endoscopic endonasal approach to the remove pituitary macroadenoma was performed subsequently. After the resection of the pituitary macroadenoma, pathology showed positive staining of growth hormone and prolactin. Insulin-like growth factor-1 normalized as well. CONCLUSIONS: Suppressed growth hormone after oral glucose tolerance test cannot exclude acromegaly, and some patients may have only mild or no clinical presentation of acromegaly. Patients with pituitary microadenoma or macroadenoma and elevated insulin-like growth factor-1 should be closely monitored for signs/symptoms of acromegaly and hypopituitarism.