Correlations Between Change Scores of Measures for Muscle Strength and Motor Function in Individuals with Spinal Muscular Atrophy Types 2 and 3

The purpose of this study was to examine the correlations between change scores on the Manual Muscle Test for muscle strength and the Gross Motor Function Measure for motor function in individuals with spinal muscular atrophy type 2 and type 3. The specific aims were to reveal any differences in correlations between younger (children) and older (adolescents and adults) individuals and also between walkers and nonwalkers with spinal muscular atrophy.A total of 56 individuals with spinal muscular atrophy aged 5 to 41 yrs were recruited. Muscle strength and motor function were measured three times at 6-mo intervals. The Manual Muscle Test scores of 36 muscle groups and Gross Motor Function Measure scores were obtained. Differences in these scores over time (baseline to 6 mos and baseline to 12 mos) were calculated.Changes in Manual Muscle Test scores correlated positively to changes in Gross Motor Function Measure scores over 12 mos (r = 0.35, P = 0.01). Significantly positive correlations between the change scores over 12 mos were evident in the older group (r = 0.48, P = 0.02) and in nonwalkers (r = 0.47, P < 0.001).The correlations between change scores on Manual Muscle Test and on Gross Motor Function Measure suggest that these two measures are suitable for representing concurrent changes in muscle strength and motor function in spinal muscular atrophy within 12 mos.