Quantitative Whole-Body Muscle MRI in Adults With Spinal Muscular Atrophy-A Sensitive Tool for Long-Time Evaluation of Disease Progression.

BACKGROUND

Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by progressive muscle weakness due to SMN protein deficiency. While effective therapies exist, their impact on slowly progressive adult SMA patients remains unclear. Reliable biomarkers for monitoring disease progression and treatment response are urgently needed. This pilot study evaluated the utility of longitudinal quantitative muscle MRI (qMRI) to monitor disease progression in adult SMA patients treated with nusinersen over an extended period.

METHODS

Nine adult patients with genetically confirmed 5q-SMA underwent whole-body muscle MRI and clinical assessment, including the Hammersmith Functional Motor Scale-Expanded (HFMS-EXP), Revised Upper Limb Module (RULM), and 6 min walk test (6MWT). Muscular fat fraction (mFF) was quantified in 20 muscles over a median follow-up of 54 months.

RESULTS

Baseline mFF correlated strongly with clinical measures (HFMS-EXP: r = -0.90, p = 0.001; 6MWT: r = -0.96, p < 0.001), but not with age at onset or age at MRI. Over the observation period, a significant increase in mFF was detected (averaged annual increase of all studied muscles: 0.47%, p = 0.011), accentuated in the lower leg muscles. In contrast, clinical measures showed no consistent change. Consequently, no significant correlations were found between changes in mFF and clinical scores.

CONCLUSIONS

This study provides the longest reported longitudinal qMRI assessment in adult SMA patients treated with nusinersen, demonstrating that mFF progressively increases despite stable clinical scores. The results suggest that qMRI may be a sensitive and objective biomarker for detecting subtle disease progression in adult SMA, potentially surpassing clinical measures.