Bone mineral density and body composition before and during treatment with gonadotropin-releasing hormone agonist in children with central precocious and early puberty

Major changes in bone mineral density (BMD) and body composition occur during puberty. In the present longitudinal study, we evaluated BMD and calculated volumetric BMD [bone mineral apparent density (BMAD)], bone metabolism, and body composition of children (32 girls and 2 boys) with central precocious and early puberty before and during treatment with GnRH agonist (GnRH). Patients were studied at baseline and during treatment for 6 months (n = 34), 1 yr (n = 33), and 2 yr (n = 16). Lumbar spine and total body BMD and body composition were measured with dual-energy x-ray absorptiometry. The variables were compared with age-and sex-matched reference values of the same population and expressed as SD score (SDS). Bone age was assessed. Serum calcium, phosphate, alkaline phosphatase, osteocalcin, the carboxyterminal propeptide of type I collagen (PICP), cross-linked telopeptide of collagen I (ICTP), 1,25 dihydroxyvitamin D and urinary hydroxyproline/creatinine, and calcium/creatinine ratios were measured. Mean lumbar spine BMD SDS was significantly higher than zero at baseline (P < 0.02) and did not differ from normal, after 2 yr of treatment. Mean spinal BMAD SDS and total body BMD SDS were not significantly different from zero at baseline and had not changed significantly after 2 yr of treatment. During therapy, fat mass and percentage body fat SDS increased, whereas lean tissue mass SDS decreased. Mean lumbar spine BMD and BMAD and total body BMD SDS, calculated for bone age, were all lower than zero at baseline (BMD P < 0.001 and BMAD P < 0.05) and also after 2 yr treatment (respectively, P < 0.001, P < 0.05, and P < 0.01). Biochemical bone parameters were significantly higher than prepubertal values at baseline, and they decreased during treatment. In conclusion, patients with central precocious and early puberty had normal BMD for chronological age but low BMD for bone age, after 2 yr of treatment with GnRH. Bone turnover decreased during treatment. Changes in body composition resembled those seen in patients with GH deficiency.