Growth hormone response to a growth hormone-releasing hormone stimulation test in a population-based study following cranial irradiation of childhoodbrain tumors

Children with brain tumors are at high risk of developing growth hormone de ficiency (GHD) after cranial irradiation (CI) if the hypothalamus/pituitary (HP) axis falls within the fields of irradiation. The biological effective dose (BED) of irradiation to the HP region was determined, since BED gives a means of expressing the biological effect of various irradiation treatme nt schedules in a uniform way. Hypothalamic versus pituitary damage as caus e of GHD was distinguished in 62 patients by comparing the growth hormone ( GH) peak response to an insulin tolerance test (ITT)/arginine stimulation t est and the GH response to a growth hormone-releasing hormone (GHRH) stimul ation test. Peak GH response to a GHRH test was significantly higher (media n 7.3 mU/l; range: 0.5-79.0 mU/l) than that of an ITT/arginine test (median 4.7 mU/l; range: 0.01-75.0 mU/l) (p = 0.017). Peak GH after a GHRH test wa s significantly inversely correlated to follow-up time (r(x) = -0.46, p < 0 .0001) and to BED (R-s = -0.28, p = 0.03), and both were found to be of sig nificance in a multivariante regression analysis. We speculate that a signi ficant number of patients developed hypothalamic radiation-induced damage t o the GHRH secreting neurons, and secondary to this the pituitary gland dev eloped decreased responsiveness to GHRH following CI in childhood. Copyrigh t (C) 2001 S. Karger AG. Basel.