Background Spinal muscular atrophy (SMA) is a genetic disease of the anterior horn
cell with a frequency of 8 per 100 000 live births and a high rate of
mortality during infancy. The American Spinal Muscular Atrophy Randomized
Trials (AmSMART) Group is an organization of 5 centers formed to perform clinical
trials in children with SMA.
Objective To devise reliable methods to measure strength, motor function, lung
function, and quality of life for use as outcome measures in children with
SMA.
Setting Tertiary referral center, pediatric neurology department.
Patients and Methods Twelve children with SMA aged 2 to 14 years were enrolled in a reliability
study of 4 outcome measures: quantitative muscle testing (in children >5 years),
gross motor function measure, pulmonary function tests, and quality of life.
The Richmond Quantitative Measurement System was used to test grip, knee flexion
and extension, and elbow flexion. Gross motor function measure was performed
as described, and pulmonary function tests were measured using the KoKo system.
Quality of life was assessed via the PedsQL and the PedsQL Neuromuscular Module
for patients and parents.
Results Ten children fulfilled the inclusion criteria and completed at least
3 visits with 3 evaluators in 6 months. Using a weighted 
, the gross
motor function measure showed high interrater reliability. Quantitative muscle
testing showed greater variability among the weakest children; the findings
for pulmonary function tests and quality of life were inconclusive. The PedsQL
Neuromuscular Module for parents had moderately high reliability.
Conclusion A tool for motor function may be more useful in clinical trials of childhood
SMA than one for quantitative muscle strength.
