Assessing MScanFit MUNE in Amyotrophic Lateral Sclerosis: Influence of Nerve Conduction Distance and Temporal Dispersion.

Introduction/aims: MScanFit is a promising method for motor unit number estimation (MUNE) based on compound muscle action potential (CMAP) scanning. Considering that CMAP morphology may be altered by temporal dispersion associated with nerve conduction distance, it is important to evaluate the potential impact of these changes on MScanFit measurements. Therefore, we aimed to investigate the effect of nerve conduction distance on MScanFit MUNE in patients with amyotrophic lateral sclerosis (ALS).

Methods: MScanFit MUNE was recorded from the abductor digiti minimi (ADM) muscle by stimulating the ulnar nerve at the wrist and elbow in twenty-three ALS patients. Consistency of MScanFit MUNE and size parameters, CMAP amplitude, and CMAP duration were evaluated using intraclass correlation coefficients (ICC).

Results: Significant differences were noted in CMAP amplitudes (6.35 ± 2.5 mV vs. 5.7 ± 2.4 mV; p = 0.003) and CMAP durations (5.8 ± 0.7 ms vs. 6.2 ± 0.8 ms; p < 0.001), reflecting temporal dispersion effects. MUNE values showed high consistency between wrist and elbow stimulations (61 ± 32.4 vs. 61.1 ± 30.7; p = 0.99), with an ICC of 0.86. Similar repeatability was also observed for MScanFit size parameters.

Discussion: The reliability of MScanFit MUNE in determining motor unit values in ALS patients remains consistent regardless of the stimulation distance. Our findings highlight the effectiveness of MScanFit MUNE in evaluating motor unit loss of ALS patients and demonstrate its resilience to temporal dispersion effects. Proximal stimulation serves as a viable alternative, enhancing the utility of MScanFit in clinical settings.