Predictors of Remission following Transsphenoidal Surgery for Acromegaly: Value of Early Postoperative Growth Hormone Testing

Introduction: Surgical remission for Acromegaly is dependent on several factors including tumor size, invasiveness and surgical expertise. We report on the value of early post-operative growth hormone (GH) level as a predictor of outcome and to guide early surgical re-exploration in Acromegaly in a specialist pituitary surgery unit. Methods: Patients with Acromegaly undergoing first time endoscopic transsphenoidal surgery by a single surgeon between 2005 and 2013 were studied. Insulin growth factor-1 (IGF1) and GH nadir on oral glucose tolerance test (oGTT) were tested at various time points, including 2 to 5 days postoperatively. Definition of disease remission was according to the 2010 Consensus criteria (i.e., GH nadir <0.4 μg/L following an oGTT and normalized population matched IGF-1). Results: There were 70 consecutive acromegaly patients, with 13 (19%) microadenomas and 20 (29%) noted to be invasive at surgery. Mean follow-up was 47 ± 27 months. Overall, surgical remission was achieved in 47 (67%) patients. Of 9 patients undergoing early re-exploration, 4 (44%) achieved long-term remission. Remission rates for patients with early post-op GH nadir on OGTT of less than 0.4 ( N = 36), 0.4–1 ( N = 26) and greater than 1 μg/L ( N = 8) were 89, 50, and 25%, respectively. On univariate analysis the remission rates were lower for patients with invasive adenomas (as noted on MR and at surgery, 45 vs. 76%) and higher pre-operative IGF1 (56% Vs 79%). There were non-significant trends toward lower remission rates for macro adenomas (63%) than microadenomas (85%) and for patients with a pre-op GH nadir greater than 10μg /L (58 vs. 73%). On multivariate regression analysis, pre-op IGF1 (odds ratio of 10.3) and early postop GH nadir on OGTT of 0.4 to 1 μg/L (odds ratio of 5.4) and >1 μg/L (odds ratio 40) were the significant predictors of residual disease. Conclusion: Early postoperative GH nadir on OGTT is the most useful predictor of long term disease remission and can be a guide to select patients for early re-exploration to remove residual disease.