Outcome measures for pediatric spinal muscular atrophy

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.

To devise reliable methods to measure strength, motor function, lung function, and quality of life for use as outcome measures in children with SMA.

Tertiary referral center, pediatric neurology department.

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.

Ten children fulfilled the inclusion criteria and completed at least 3 visits with 3 evaluators in 6 months. Using a weighted kappa, 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.

A tool for motor function may be more useful in clinical trials of childhood SMA than one for quantitative muscle strength.