1126 - Gait Analysis as a Supplementary Motor Function Measure in SMA Type III Post-Nusinersen: A Case Report

Case Diagnosis: Spinal Muscular Atrophy (SMA) Type III

Case Description: This report describes an eight-year-old girl with SMA Type III who presented with early motor delays and a waddling gait. Genetic testing confirmed SMN1 deletion with two SMN2 copies. At six years old, Nusinersen treatment was initiated following Taiwan FDA approval. After four loading doses, her Hammersmith Functional Motor Scale (HFMSE) score improved from 45 to 54, and her Revised Upper Limb Module (RULM) score from 33 to 36. Although these scores plateaued, she reported gains in energy, stamina, and motor function. To study this inconsistency, gait was analyzed using GaitUp during a six-minute walk test. Increased walking distances were observed. The changes of  velocity, stride length, and heel height were also studied. Compared to SMA Type III peers without treatment, her data suggests functional gains. Now, with ongoing Nusinersen and physical therapy, she can perform daily movements more independently.

Discussions: SMA is classified into types I-IV by age of onset and severity, with Type III being a milder form that allows walking ability. Nusinersen, the first FDA-approved treatment for SMA, improves survival motor neuron (SMN) protein levels and enhances motor function. Motor progression in SMA is commonly assessed with scales like the Hammersmith Functional Motor Scale-Expanded (HFMSE) and Revised Upper Limb Module (RULM). These scales capture improvements well in severe patients, yet in patients with higher baseline motor function, like Type III, scores may plateau even as functional gains continue. Our case highlights that despite plateauing HFMSE and RULM scores, the patient reported continued increases in energy and stamina with Nusinersen. This suggests a need for alternate assessments like gait analysis, as it can capture nuanced improvements. Notably, our findings provide the first pediatric gait data post-Nusinersen, showing gains compared to untreated patients.

Conclusions: Gait can be a supplementary measurement in type III SMA Post-Nusinersen.