A comparative analysis of bone mineral density in cerebral palsy and spinal muscular atrophy.

Introduction: Patients with cerebral palsy (CP) and spinal muscular atrophy (SMA) with immobility are at risk for low bone mineral density (BMD) and fragility fractures. This study investigates whether BMD differs between these two groups given their distinct pathological mechanisms. Methods: Data were collected from non-ambulatory patients diagnosed with CP (GMFCS IV-V) and SMA (type I-II), aged five years and older, who were seen at a metabolic bone clinic between January 2012 and July 2023. Dual-energy X-ray absorptiometry (DXA) assessed BMD at the lumbar spine (LS) and lateral distal femur (LDF), region 3 (R3). Z-scores were calculated and compared between groups using the Wilcoxon rank sum test. Results: This study included 274 children with CP and 16 with SMA. Unadjusted LS Z-scores were low and comparable in both groups (CP: -2.3, SMA: -2.6; p = 0.7). After adjusting for height, LS Z-scores were in the normal range (CP: -0.9, SMA: -1.6; p = 0.3). However, the SMA group had significantly lower BMD in R3 of the LDF compared to the CP group (CP: -2.9, SMA: -3.9; p = 0.047). Conclusion: Both groups had normal height adjusted LS BMD and low R3 LDF BMD, with the SMA group significantly lower. We theorize that it may be due to the differences in muscle tonicity on the bone. We recommend including the distal femur bone density in routine bone health assessments and that BMD should be adjusted for height when possible.