Impaired glucose tolerance and overt diabetes mellitus are frequently associated with acromegaly. The aim of this study was to find out whether these alterations could be reversed after transsphenoidal surgery.

Two hundred and thirty-nine acromegalic patients were studied before and 6–12 months after transsphenoidal surgery. Diagnosis of active acromegaly was established on the basis of widely recognized criteria. In each patient, glucose and insulin concentrations were assessed during the 75 g oral glucose tolerance test (OGTT). To estimate insulin resistance, we used homeostasis model assessment (HOMA-IR) and the quantitative insulin sensitivity check index (QUICKI).

At the moment of diagnosis, diabetes mellitus was present in 25% of the acromegalic patients. After surgery, the prevalence of diabetes mellitus normalized to the level present in the general Polish population. We found a statistically significant reduction after surgery in plasma glucose levels both fasting (89.45 ± 13.92 mg/dL vs. 99.12 ± 17.33 mg/dL, p < 0.001) and during OGTT. Similarly, a prominent reduction in insulin secretion was found after surgery compared to the moment of diagnosis (15.44 ± 8.80 mIU/mL vs. 23.40 ± 10.24 mIU/mL, p < 0.001). After transsphenoidal surgery, there was a significant reduction in HOMA-IR (3.08 vs. 6.76, p < 0.0001) and a significant increase in QUICKI (0.32 vs. 0.29, p < 0.001). There were no statistically significant differences after surgery in fasting glucose and insulin levels between patients with controlled and inadequately controlled disease.

We conclude that in acromegalic patients glucose homeostasis alterations and insulin sensitivity can be normalized after transsphenoidal surgery, even if strict biochemical cure criteria are not fulfilled.