Clinical features and natural course of acromegaly in patients with discordance in the nadir GH level on the oral glucose test and the IGF-1 value at 3 months after adenomectomy

Discordant GH and IGF-1 levels after adenomectomy are well recognized in acromegalics. The aim of this study was to evaluate the clinical features and natural course of postoperative acromegaly associated with discordant GH and IGF-1 levels over a postoperative period. A total of 69 acromegalics underwent surgery with at least 1 year of follow-up and received 75-g oral glucose tolerance tests (OGTTs) at 3 months postoperatively. The patients were categorized into four groups according to the postoperative nadir GH levels and IGF-1 levels: controlled group (normal GH and normal IGF-1), high-IGF-1 group (normal GH and high IGF-1), high-GH group (high GH and normal IGF-1), and uncontrolled group (high GH and high IGF-1). The incidence of discordant GH and IGF-1 levels was 27.5 %: high-IGF-1 group = 10.1 % (n = 7) and high-GH group = 17.4 % (n = 12). All patients in the high-IGF-1 group exhibited a decline in the IGF-1 level after surgery, with normalization observed in 71.4 % of the patients without additional treatment (median 23 months). These subjects had preoperatively high IGF-1 levels despite not demonstrating higher GH levels than the patients in the controlled group. On the other hand, four patients in the high-GH group exhibited an elevated nadir GH level higher than 1.0 μg/L on repeated OGTTs after 3 months, and one patient experienced a recurrence of acromegaly. Patients in the high-IGF-1 group require no additional treatments, and their IGF-1 levels are likely to normalize within a few years. However, patients in the high-GH group should be carefully followed due to the possibility of recurrence.