Progressive bone impairment with age and pubertal development in neurofibromatosis type I

Bone density impairment represents an established complication in adults with neurofibromatosis type 1, while few data exist in the pediatric population. Age- and gender-adjusted bone mass decreases with age and pubertal development, identifying childhood as the best time frame to introduce prevention strategies aiming at peak bone mass achievement.

The present study aims at evaluating bone mineral density (BMD) in a population of children with neurofibromatosis type I (NF-1), with particular focus on changes occurring during growth and pubertal development.

Bone metabolic markers and bone status [by dual-energy X-ray absorptiometry scans (DXA) of the total body and lumbar spine with morphometric analysis] were assessed in 50 children (33 males; mean age ± SD, 11.6 ± 4 years). Bone mineral apparent density (BMAD), trabecular bone score (TBS), and bone strain (BS) of the lumbar spine (LS) DXA were also obtained.

In our cohort areal BMD (aBMD) Z-score was below the mean in 88% of the patients at LS (70% after correction for bone size) and in 86% considering total body (TB) DXA. However, aBMD Z-score was < - 2 in 12% after correction for bone size at LS and TB, respectively. Lumbar spine aBMD Z-score (r = - 0.54, P < 0.0001), LS BMAD Z-score (r = - 0.53, P < 0.0001), and TB Z-score (r = - 0.39, P = 0.005) showed a negative correlation with growth and pubertal development (P = 0.007, P = 0.02, P = 0.01, respectively), suggesting that patients failed to gain as much as expected for age.

Bone density impairment becomes more evident with growth and pubertal development in NF-1 patients, thus identifying childhood as the best time frame to introduce prevention strategies aiming at peak bone mass achievement. TBS and BS, providing bone DXA qualitative information, could be useful during longitudinal follow-up for better characterizing bone impairment in these patients.