Reduced bone mineral density in adolescents with Duchenne Muscular Dystrophy (DMD) and scoliosis

Abstract

Duchenne muscular dystrophy is a progressive disease usually associated with loss of ambulation and progressive scoliosis. Immobilisation and glucocorticoid treatment are predisposing factors for reduced bone mineral density (BMD). Analysis of quantitative computed tomography revealed low BMD in thoracic and lumbar vertebrae in comparison to age- and sex-matched healthy controls.

Introduction: Evaluation of vertebral bone mineral density (BMD) in Duchenne Muscular Dystrophy (DMD) adolescents with untreated advanced scoliosis and comparison with the BMD values of healthy age-matched controls, based on quantitative computer tomography.

Methods: Thirty-seven DMD adolescents (age 15.6 ± 2.5 years) with spinal deformity were evaluated clinically and radiologically prior to definite spinal fusion and compared to 31 male and age-matched healthy individuals (age 15.7 ± 2.3 years). Data related to previous medical treatment, physiotherapy and ambulatory status was also analysed. Scoliotic curves were measured on plain sitting radiographs of the spine. The BMD Z-scores of the thoracic and lumbar vertebrae were calculated with QCTpro® (Mindways Software Inc., USA), based on data sets of preoperative, phantom pre-calibrated spinal computed tomography scans.

Results: A statistically significant lower BMD could be found in DMD adolescents, when compared to healthy controls, showing an average value for the lumbar spine of 80.5 ± 30.5 mg/cm³. Z-scores deteriorated from the upper thoracic towards the lower lumbar vertebrae. All but the uppermost thoracic vertebrae had reduced BMD values, with the thoracolumbar and lumbar region demonstrating the lowest BMD. No significant correlation was observed between BMD and the severity of the scoliotic curve, previous glucocorticoid treatment, cardiovascular impairment, vitamin D supplementation, non-invasive ventilation or physiotherapy.

Conclusion: DMD adolescents with scoliosis have strongly reduced BMD Z-scores, especially in the lumbar spine in comparison to healthy controls. These findings support the implementation of a standardised screening and treatment protocol. Level of evidence/clinical relevance: therapeutic level III.

Keywords: BMD; Bone mineral density; DMD; Duchenne Muscular Dystrophy; Glucocorticoid treatment; Osteoporosis; QCT; Scoliosis; Z-score.

Fig. 1

Anteroposterior (ap) (a) and lateral sitting radiographs (b) of a 12-year-old DMD patient with rapid progression of scoliosis within 18 months (c,d)

Fig. 2

Software QCTpro® for evaluating BMD. A The red and yellow areas show the ROI in the three anatomical planes, which should exclude cortical bone and neurovascular structures. B BMD results of the lumbar spine for a DMD patient, with Z-scores being provided based on normal values of the UCSF database [–13]

Fig. 3

BMD values of each thoracic and lumbar vertebra of the DMD (n = 37, blue) and healthy control group (n = 31, grey); T = thoracic; L = lumbar; numbers in columns equal n; ***p < 0.001

Fig. 4

Average BMD Z-scores (blue) for DMD patients (n = 37) for each thoracic and lumbar vertebra. From the healthy age- and sex-matched healthy control group (n = 31) calculated Z-score thresholds for critical BMD values of 120 mg/cm³ (orange) and 80 mg/cm³ (red), respectively. A significant deterioration of BMD values is shown for the lower thoracic and lumbar region. T = thoracic; L = lumbar