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Published on: March 4, 2014
Bone Fragility and Fracture Characteristics in Patients With Spinal and Bulbar Muscular Atrophy
Takahiro Kawase1, Shinichiro Yamada1, Yoshiyuki Kishimoto1
1Department of Neurology, Nagoya University Graduate School of Medicine, Nagoya, Japan.
Background:
Spinal and bulbar muscular atrophy (SBMA) is a hereditary neuromuscular disorder linked to androgen receptor gene mutations, often associated with metabolic abnormalities. We aimed to investigate the incidence of fragility fractures and the underlying mechanisms in SBMA.
Methods:
Consecutive genetically confirmed SBMA patients and healthy controls (HC) were enrolled. We surveyed fracture history and assessed motor function, bone metabolism markers, and bone mineral density (BMD) using dual-energy X-ray absorptiometry. Longitudinal BMD changes were also analyzed between SBMA patients and HC.
Results:
A total of 109 SBMA patients and 21 HC were included. Fragility fractures in SBMA patients were mainly observed in cortical bone-dominant regions. Their lower limb BMD was significantly reduced (SBMA 1.10 g/cm, HC 1.19 g/cm; p < 0.05) and further decreased overtime. Despite low bone resorption markers, bone formation markers showed no difference between the groups, suggesting that SBMA patients exhibit characteristics of low turnover osteoporosis. Serum 25-hydroxyvitamin D levels were lower in SBMA patients than in HC (15.4 ng/mL vs. 19.4 ng/mL; p < 0.01). Longitudinal analysis revealed that SBMA patients had a higher incidence of fragility fractures than HC (log-rank test, p < 0.05), with the first fragility fracture occurring 10 years after the onset of muscle weakness. Low baseline BMD was a predictor of fragility fractures (adjusted OR = 0.32; 95% CI: 0.17-0.60; p < 0.05).
Conclusions:
SBMA patients have a high fragility fracture incidence, particularly in cortical bone, with a progressive BMD decrease. Low bone turnover and vitamin D deficiency are associated with these fractures.
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