Compound Muscle Action Potential (CMAP) Amplitude Trajectories and Pattern in Adults with 5q-Spinal Muscular Atrophy...

Area of Science:

• Neurology
• Clinical Electrophysiology
• Rare Diseases

Background:

• Spinal muscular atrophy (SMA) is a rare genetic neuromuscular disorder.
• Nusinersen is an approved treatment for SMA.

Purpose of the Study:

• To evaluate changes in compound muscle action potential (CMAP) amplitude in adults with SMA during nusinersen treatment.
• To assess the association between CMAP amplitude and motor function improvements.

Main Methods:

• A multicenter study followed 78 adult SMA patients for up to 4.5 years.
• Median, ulnar, and peroneal CMAP amplitudes were measured.
• Motor function was assessed using the Revised Upper Limb Module (RULM) and Hammersmith Functional Motor Scale Expanded (HFMSE).

Main Results:

• CMAP amplitudes showed no significant changes over time and did not differ between SMA types 2 and 3.
• Baseline CMAP values showed potential in distinguishing SMA types.
• No significant correlations were found between changes in CMAP and motor function scores (RULM, HFMSE).

Conclusions:

• CMAP amplitudes are stable during nusinersen treatment in adult SMA patients.
• CMAP amplitude correlates with SMA disease severity but is not a sensitive biomarker for treatment response.
• Further research may explore other biomarkers for treatment efficacy.