Low insulin resistance after surgery predicts poor GH suppression one year after complete resection for acromegaly: a retrospective study

Abstract

Remission of acromegaly is defined as a nadir in GH <1.0 ng/mL during a 75-g oral glucose tolerance test (75gOGTT) and insulin-like growth factor-1 (IGF-1) normalization. Recently, a lower cut-off value for GH nadir (<0.4 ng/mL) has been proposed. We retrospectively evaluated the prevalence and clinical characteristics of postoperative cases with normalized IGF-1 levels and a GH nadir of 0.4-1.0 ng/mL one year after complete resection of GH-secreting pituitary adenoma (GHoma). We included 110 cases of acromegaly with complete adenoma resection, no preoperative treatment, preoperative glycosylated hemoglobin <6.5%, preoperative basal plasma glucose <126 mg/dL, GH nadir <1.0 ng/mL during a 75gOGTT, and normalized IGF-1 at the first postoperative year evaluation, whereupon patients were divided into two groups: control (GH nadir <0.4 ng/mL) and high GH (GH nadir >0.4 ng/mL). Clinical parameters, including measures of insulin secretion and resistance, were compared between groups. The high GH group included 10 patients (9.1%) and had a lesser level of insulin resistance immediately following surgery and at the first postoperative year evaluation. On single regression analysis, insulin resistance immediately following surgery was predictive of and correlated with the GH nadir at the first postoperative year evaluation. The GH nadir at the first postoperative year evaluation may be insufficient in patients with normalized IGF-1 with low insulin resistance immediately following complete resection of GHoma. Careful evaluation is needed to assess remission in such patients.