Bone Abstracts

Objectives: Neurofibromatosis 1 (NF1) is one of the most common autosomal dominant diseases. Skeletal involvement such as short stature, kyphoscoliosis, tibial bowing and pseudarthrosis are common osseous manifestations of NF1. Moreover, there is a growing evidence that reduced bone mineral density (BMD), is a common feature of NF1 subjects. The aim of the study was to evaluate the usefulness of Bone Mineral Density and Quantitative Ultrasound (QUS) at phalanxes in the assessment and monitoring of bone status in NF1 subjects.

Methods: We studied 51 patients (age: 8.4±5.2 years) with NF1 and 41 age and sex-matched controls. In all subjects bone mineral density at lumbar spine (BMD-LS), at femoral neck (BMD-FN) and at total femur (BMD-T) was measured by using a DXA machine (Hologic QDR 4500). Moreover QUS parameters at phalanxes by Bone Profiler-IGEA (amplitude dependent speed of sound: AD-SoS and bone transmission time: BTT) were assessed. A subgroup of 34 patients with NF1 and 27 controls were followed longitudinally (follow up period: 3.5±2.7 years).

Results: In NF1 subjects the values of BMD were significantly lower than in controls at all skeletal sites. In NF1 subjects BMD values, expressed as z-scores, were −0.270±1.03; −0.699±1.06 and −0.577±1.11 for lumbar spine, femoral neck and total femur, respectively. All QUS parameters were significantly reduced in NF1 subjects; the lowest values were observed for BTT (Z-score= −0.315±0.8) and AD-SoS (Z-score =−0.470±1.2). The NF1 subjects were separated in groups with (27.5%) and without (72.5%) skeletal abnormality. The subjects with skeletal abnormality had a decrease in densitometric parameters that reached the statistical significance for BMD-FN and BMD-T respectively (P<0.05), but not for BMD-LS. During the longitudinal study the NF1 subjects presented a worsening of either BMD values, expressed as Z-score or QUS parameters namely BTT and AD-SoS Z-score.

Conclusions: Our findings indicate that young NF1 patients have statistically significant decreased BMD and QUS values compared with controls and that the presence of skeletal abnormalities seems to be associated with a greater impairment in bone status. The longitudinal study has shown that in NF1 subjects both BMD and QUS remained significantly lower with respect to age-matched controls.

Disclosure: The authors declared no competing interests.