Researchers studying boys with Duchenne muscular dystrophy (DMD) found that muscle weakness, contractures and size changes do not follow a simple downward trajectory, according to results from a study published recently in PLOS One.
Instead, these impairments often begin with a period of stability or slight improvement before worsening at different ages. Understanding this pattern can help patients and caregivers anticipate changes and potentially improve early strategies for intervention.
“[T]his study has established longitudinal trajectories of muscle impairments, consisting of muscle weakness, contractures, and muscle size alterations, in a cohort of growing boys with DMD covering the ambulation period. Moreover, the results provided enriched historical data and revealed promising outcome measures that could enhance the detection of the efficacy of novel therapeutic strategies,” explained the authors of this study. They continued, “However, future large-scale multicenter studies with larger sample sizes are necessary to assess the impact of clinical and medical background differences among boys with DMD.”
This study followed 33 boys with DMD between the ages of 4.3 and 17, using specialized tools to measure lower limb muscle strength, flexibility and size. A total of 161 strength assessments, 178 flexibility tests and 64 muscle ultrasound scans were conducted. Researchers compared the results to typically developing children, allowing them to measure the extent of muscle impairment over time.
Read more about the prognosis of DMD
Early in the disease, at ages 4.3 to 4.9 years, boys with DMD already showed muscle weakness and reduced flexibility in key areas, such as ankle dorsiflexion, hamstring flexibility and hip extension. However, muscle size in some areas, such as the medial gastrocnemius (a calf muscle), was larger than normal. Strength and flexibility remained relatively stable until ages 6.6 to 9.4 years, after which muscle loss became more pronounced.
The decline accelerated in later years, with hip, knee and ankle strength decreasing by 0.27 to 0.45 standard units per year. Ankle flexibility worsened steadily, dropping by 0.23 to 0.33 standard units annually. Muscle size also shrank, particularly in the medial gastrocnemius and rectus femoris (a key thigh muscle), which declined by 0.56 and 0.36 standard units per year, respectively.
These results highlight the importance of early intervention and the need for therapies that target muscle preservation before the decline begins. By establishing detailed muscle impairment trajectories, this study provides essential data for future research and clinical trials. The insights gained could help refine treatments aimed at maintaining mobility and delaying the progression of muscle loss in patients with DMD.
While further studies are necessary to confirm these results, the data offer a valuable resource for doctors, researchers, and families affected by DMD. Understanding when and how muscle deterioration occurs could lead to more effective treatments, ultimately improving the quality of life for individuals with the disease.
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