Impaired glucose metabolism in Japanese patients with acromegaly is restored after successful pituitary surgery if pancreatic β-cell function is preserved

Objective: Impaired glucose metabolism is common in acromegaly, but it is not clear how glucose metabolism is impaired or what predicts its restoration after cure of the disease. To identify factors involved in the impairment of glucose metabolism in acromegaly, we evaluated clinical parameters before and immediately after surgical cure of the disease. Design and methods: We retrospectively analyzed clinical data of 92 consecutive Japanese patients with acromegaly who underwent successful pituitary surgery. Patients who had received medical therapy for acromegaly or insulin treatment for diabetes were excluded. We evaluated insulin resistance (IR) and pancreatic beta-cell function in addition to GH and IGF1 levels before and after surgery. Results: In this study of Japanese patients with acromegaly, average body mass index (BMI) was 23.4, and no patient had a BMI > 30. IR was involved in the impairment of glucose metabolism, which was restored upon surgical cure of acromegaly if beta-cell function was preserved. Insufficient beta-cell function did not improve after normalization of GH/IGF1 and was associated with impaired glucose metabolism before and after surgery. Results of receiver operating characteristic analysis of preoperative clinical parameters suggest that insulinogenic index (IGI) > 0.50 best predicts restoration of normal glucose metabolism upon cure of acromegaly in Japanese patients. Conclusions: IR impairs glucose metabolism in acromegaly. Once beta-cell function is impaired, abnormal glucose metabolism persists even after cure of acromegaly. IGI > 0.50 indicates that beta-cell function is preserved in non-obese Japanese patients with acromegaly.