Bioelectrical Impedance Analysis Can Be a Useful Screen for Excess Adiposity in Spinal Muscular Atrophy

Accurate, noninvasive measures of body composition are needed for management of patients with spinal muscular atrophy. Fat mass index (fat mass/height(2) in kg/m(2)) was measured in 16 subjects with spinal muscular atrophy using 5 bioelectrical impedance analysis equations and compared with a reference method, dual-energy x-ray absorptiometry. The machine default equation, validated by Cordain, was the primary analysis. Fat mass index calculated by impedance measures differed by between -2.5 kg/m(2) and 1.7 kg/m(2) from the reference mean (8.3 +/- 5.0 kg/m(2)). The Cordain equation provided the smallest difference (-0.4 +/- 2.0 kg/m(2)), with correlation coefficient of 0.92. The Cordain equation showed high sensitivity (85.7%) and specificity (100%) for prediction of "at risk for overweight" (fat mass index > 85th percentile for age and gender). Although insufficiently accurate for use as a research tool, bioelectrical impedance can have application as a well-tolerated, noninvasive, easily used screening tool for excess adiposity in patients with spinal muscular atrophy.