Low bone mineral density in spinal muscular atrophy

Background and Purpose: Pathological fractures are common in pediatric neuromuscular disorders. Dual-energy x-ray absorptiometry has become the most accepted technique for the measurement of bone mineral density (BMD) in adults and children. Limited data are available on BMD in pediatric neuromuscular diseases except Duchenne muscular dystrophy. Methods: We retrospectively analyzed the results of all dual-energy x-ray absorptiometry scans done in a period of 23 months at a tertiary care pediatric neuromuscular center. BMD was performed on spine region L1-4. Osteopenia was classified as mild if the Z scores were between 0 and -1.5, moderate if Z scores were between -1.5 and -2.5, and severe if Z scores were > -2.5 standard deviation scores. Results: Eighty-four dual-energy x-ray absorptiometry scans were performed on 79 patients between the ages of 4 months and 18 years with the mean age of 8 years. Z scores were used to compare their BMDs. BMD was lowest in patients with spinal muscular atrophy (SMA) with Z score of -2.25 ± 0.31 standard deviation scores. The Z score for patients with Duchenne muscular dystrophy was -1.72 ± 0.1. The BMD in nonambulatory patients with SMA was significantly decreased compared with ambulatory patients with SMA (P < 0.05). Conclusions: We conclude that osteopenia is common in children with neuromuscular disorders. Patients with SMA have the lowest BMD.