CRANIAL IRRADIATION AND EARLY PUBERTY

Abstract

Low doses of cranial irradiation (1800-2400 cGy) employed in the management of acute lymphoblastic leukaemia may cause early or precocious puberty in girls but not boys. To determine if this sexual dichotomy exists at higher irradiation doses (2500-4700 cGy) the onset of puberty was identified in 46 children (30 male), previously irradiated for a brain tumour not involving the hypothalamic-pituitary axis, and compared with the normal pubertal standards of Tanner. Regression analysis was employed to assess whether tumour diagnosis, sex, age at irradiation, chemotherapy, use of GH before puberty and radiotherapy protocol influenced age at pubertal onset. The onset of puberty occurred at an early age in both sexes (mean 8.5l years in girls and 9.21 years in boys plus 0.29 years for every year of age at irradiation). In the context of GH deficiency which is usually associated with a delay in the onset of puberty this is abnormal. There was a significant linear association between age at irradiation and age at onset of puberty in both sexes. At each age of irradiation the estimated age at the onset of puberty was approximately 0.7 years earlier in girls than boys. A similar trend was seen for bone age, which was abnormally early at the time of pubertal onset (mean 7.39 years in girls and 8.66 years in boys plus 0.25 years for every year of age at the time of irradiation). Radiation induced early puberty is not restricted to females at the doses of irradiation employed in the treatment of brain tumours. The clinical consequence of early puberty in the management of poor growth associated with radiation induced GH deficiency is to foreshorten the time available for treatment with GH.