Bone Mineral Density Assessment by Quantitative Computed Tomography in Glucocorticoid-Treated Boys With Duchenne Muscular Dystrophy: A Linear Mixed-Effects Modeling Approach

Abstract

Objective: Boys with Duchenne muscular dystrophy (DMD) are at risk of bone damage and low bone mineral density (BMD). The aim of the study is to examine lumbar BMD values measured by QCT and identify the factors associated with BMD loss using a multilevel mixed-effects model.

Methods: Lumbar BMD was evaluated by quantitative computed tomography (QCT) at diagnosis, 1 and 2 years follow up in patients with DMD who were treated with GC. Demographic data, functional activity scores (FMSs), laboratory parameters and steroid use were recorded. A multilevel mixed-effects model was used to analyze BMD loss.

Results: Nineteen patients with DMD who had a total of sixty complete records between January 2018 and October 2021 were retrospectively analyzed. At baseline, 15.8% of patients (3/19) had low lumbar BMD (Z score ≤ -2), and the mean BMD Z score on QCT was -0.85 (SD 1.32). The mean BMD Z score at 1 and 2 years postbaseline decreased to -1.56 (SD 1.62) and -2.02 (SD 1.36), respectively. In our model, BMD Z score loss was associated with age (β=-0.358, p=0.0003) and FMS (β=-0.454, p=0.031). Cumulative GC exposure and serum levels of calcium, phosphorus, 25(OH)-vitamin D and creatinine kinase did not independently predict BMD loss.

Conclusions: This study demonstrates that in DMD patients, lumbar BMD decreased gradually and progressively. Age and FMS are the main contributors to BMD loss in boys with DMD. Early recognition of risk factors associated with BMD loss may facilitate the development of strategies to optimize bone health.

Keywords: Duchenne muscular dystrophy; bone mineral density; glucocorticoids; osteoporosis; quantitative computed tomography.

Figure 1

(A) Images for a 7-year-old boy with DMD who has been treated with GC for 2 years. The measurements of L1, L2, and L3 vertebral trabecular volumetric bone mineral density (BMD) are shown. The BMD of L1, L2, and L3 is 133.49 mg/cm³, 130.73 mg/cm³, and 135.56 mg/cm³, respectively; the average lumbar volumetric BMD is 133.26 mg/cm3, and the Z score is -1.55. (B) The same boy with DMD was followed up after 1 year of GC therapy. The measurements of L1, L2, and L3 vertebral trabecular volumetric bone mineral density (BMD) are shown; the BMD of L1, L2, and L3 is 128.42 mg/cm³, 116.83 mg/cm³, and 117.31 mg/cm³, respectively. The average lumbar volumetric BMD is 121.19 mg/cm3, and the Z score is -1.97.

Figure 2

Longitudinal changes lumbar intrabecular BMD (A) and lumbar BMD Z score (B) at baseline and follow-up.