GH deficiency in patients irradiated for acromegaly: significance of GH stimulatory tests in relation to the 24 h GH secretion

Abstract

Background: Radiotherapy for pituitary adenomas frequently leads to GH deficiency (GHD). The characteristics of GH secretion in GHD induced by postoperative radiotherapy for acromegaly are not known. Hypothesis: In the long term, stimulated and spontaneous GH release is not different between patients with GHD treated by postoperative radiotherapy for acromegaly or for other pituitary adenomas. Design/subjects: We compared the characteristics of basal and stimulated GH secretion in patients with GHD, who had previously received adjunct radiotherapy after surgery for GH-producing adenomas (n=10) vs for other pituitary adenomas (n=10). All patients had a maximal GH concentration by insulin tolerance test (ITT) of 3 μg/l or less, compatible with severe GHD. Mean time after radiation was 17 and 18.7 years, respectively. Stimulated GH release was also evaluated by infusion of growth hormone-releasing hormone (GHRH), GHRH–arginine and arginine, and spontaneous GH by 10 min blood sampling for 24 h. Pulse analyses were performed by Cluster and approximate entropy. Outcomes: There were no differences between both patient groups in stimulated GH concentrations in any test. Spontaneous GH secretion was not different between both patient groups, including basal GH release, pulsatility and regularity. Pulsatile secretion was lost in two acromegalic and three non-acromegalic patients. Insulin-like growth factor-I (IGF-I) was below −2 s.d. score in nine patients in each group. Conclusion: Acromegalic patients treated by surgery and postoperative radiotherapy with an impaired response to the ITT do not differ, in the long term, in GH secretory characteristics from patients treated similarly for other pituitary tumors with an impaired response to the ITT. The ITT (or the GHRH–arginine test) is therefore reliable in establishing the diagnosis of GHD in patients treated for acromegaly by surgery and radiotherapy.