Low Bone Density Raises Risk of Fractures in DMD Boys With Scoliosis
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Boys with Duchenne muscular dystrophy (DMD) who cannot walk and have advanced scoliosis are at a higher risk of vertebral fractures due to significantly reduced bone mineral density (BMD), especially in the lumbar region of the spine, a study shows.
Their low bone density may be associated with immobilization due to disease-associated progressive muscle weakness, but it was not linked to any of the potential influencing factors evaluated, such as scoliosis severity, previous glucocorticoid treatment, vitamin D supplementation, and heart disease.
Since lower bone density may reduce the efficacy of surgery to correct scoliosis, standardized screening and treatment should be defined and implemented in this patient population, researchers noted.
The study, “Reduced bone mineral density in adolescents with Duchenne Muscular Dystrophy (DMD) and scoliosis,” was published in the journal Osteoporosis International.
Mostly affecting boys, DMD is characterized by progressive muscle degradation, inflammation, and the replacement of muscle with fat tissue, all leading to muscle weakness.
Over time, this muscle weakness results in disease symptoms such as the loss of walking ability (at about 10 years of age), and subsequent development of progressive scoliosis, which is associated with weakness in the muscles that support the spine.
After developing scoliosis, corrective surgery involving spinal fusion is typically the only solution. However, DMD is associated with a higher risk of bone fragility and fractures, which may hamper screw placement and anchorage, and limit the corrective potential of spinal fusion.
In DMD, loss of weight-bearing activity such as walking and side effects of prolonged glucocorticoid treatment are known predisposing factors for reduced bone mineral density — which increases the risk of bone fractures, including of the vertebrae.
Slowly progressing vertebral fractures without symptoms account for nearly half of low-BMD vertebral fractures and “remain unnoticed in up to one-third of patients,” the researchers wrote.
Glucocorticoids, or corticosteroids, are a type of standard immunosuppressive treatment in DMD care and are associated with slower disease progression and prolonged mobility.
Now, a team of researchers at the University Medical Center Goettingen, in Germany, evaluated whether boys with DMD with advanced scoliosis had reduced BMD in thoracic and lumbar vertebrae relative to age-matched boys without the disorders, who were served as controls.
The analysis included a total of 37 patients, with a mean age of 15.6 years, who were about to undergo corrective surgery for their scoliosis between 2017 and 2021, as well as 31 boys who were 15.7 years old on average and who did not have DMD or scoliosis.
Bone mineral density was assessed with quantitative computer tomography (CT), whose fine slice scans are thought to overcome inherent limitations of the indirectly calculated BMD obtained through the standard bone density scan called dual-energy x-ray absorptiometry, “in cases of growing patients and severe spinal deformity,” the researchers wrote.
Patients had lost their ability to walk at the average age of 9.8 years, at least five years prior to the CT examinations, and glucocorticoid treatment had been discontinued at about four years prior to their CT scans.
Results showed that, compared with controls, boys with DMD had significantly lower BMD in all evaluated vertebrae, and reduced bone mass in all but the two uppermost thoracic vertebrae. There was a clear deterioration from the upper thoracic vertebrae toward the lower lumbar vertebrae — which therefore had the highest fracture risk.
Notably, the researchers found no significant associations between BMD in Duchenne patients and potential influencing factors, including scoliosis severity, prior glucocorticoid treatment, cardiovascular impairment, vitamin D supplementation, noninvasive ventilation, and physiotherapy.
The lack of a link with prior glucocorticoid treatment was consistent with results from a previous study in DMD patients who could no longer walk independently, and may be related to the long interval between the last treatment dose and CT scans, which can dilute the therapy’s effects on bone health.
These findings suggest that adolescent boys with DMD and advanced scoliosis have a “high risk for vertebral fractures due to low bone mineral mass,” and that “whilst awareness on this subject is internationally increasing, there is still need for standardized and widely accepted screening and treatment protocols,” the team wrote.
Future studies that also include patients with milder scoliosis and a control group with matching scoliosis are needed to confirm these findings and the mechanisms and factors behind low bone mineral density in DMD.
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