Individuals with Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy have impaired bone health and increased fracture risk due to several factors including immobility, abnormal calcium metabolism, low vitamin D levels, and the inability to perform weight-bearing activities. Most patients with DMD are treated with systemic steroids (prednisone 1mg/kg/day) starting around age five to improve muscle strength, preserve lung function, and help them maintain ambulatory status. However, chronic steroid use leads to increased fragility fractures and suppresses longitudinal bone growth.

Studies suggest that early recognition and preventive treatment of osteoporosis in DMD patients improves quality of life and prolongs life expectancy; thus, there is a need for studies that evaluate the effect of available osteoporosis treatments in this at-risk population.

Herein, we investigate the value of systemic bisphosphonate use in muscular dystrophy patients by reviewing their effects on bone density as measured by dual energy X-ray absorptiometry (DXA).

Methods:

We performed a retrospective chart review using data from the Muscular Dystrophy Association (MDA) clinic which consists of DMD and Becker muscular dystrophy patients who undergo bone density screening using a GE Lunar DXA machine. Z-scores are based on the US standards for 5-26 year old healthy males as per protocol. Ninety five male MDA patients were identified. Those under 5 and over 21 years of age and those that did not undergo DXA scan after one year of therapy were excluded. Eleven patients on systemic bisphosphonate therapy (oral alendronate 1 mg/kg/dose weekly (n=9) or intravenous (IV) zoledronic acid 0.05mg/kg/dose (n=2) every 6 months) were used in our analysis. We followed the DXA scans of these patients for one year after which z-scores of the lumbar spine (L1-L4) before and one year after treatment were compared using paired sample t-tests.

Results:

Eleven patients underwent systemic bisphosphonate treatment while on chronic corticosteroid therapy. The mean pre-treatment lumbar DXA z-score was -2.5±1.9 (range -5.8 to 0). Subjects received systemic bisphosphonate therapy for a mean of 19.8±7.4 months (range 12-35 months) prior to re-evaluation with DXA. The mean DXA z-score increased by 0.37±1.5. However, a paired sample t-test revealed that there was no significant change in lumbar DXA z-scores in the subjects after bisphosphonate therapy (-2.5±1.9 versus -2.2±1.9, p=0.43). Of note, both patients on IV bisphosphonate therapy showed improvement in their lumbar spine z-scores (from -5.7 to -1.4 and from 0.0 to 0.5).

Conclusion:

There was no significant improvement in lumbar spine z-scores in patients treated with at least one year of oral bisphosphonates. However, oral bisphosphonates may still be involved in slowing the worsening of osteoporosis in this patient group, and our results may be underpowered. The limited subgroup of subjects receiving IV bisphosphonates demonstrated increased DXA z-scores, and further studies are needed to investigate the role of both IV and oral bisphosphonates in optimizing bone health in this at-risk population.