Motor unit number index (MUNIX): A novel neurophysiological technique to follow disease progression in amyotrophic lateral sclerosis

Abstract

Motor unit number estimation techniques in amyotrophic lateral sclerosis (ALS) patients are technically challenging and time-consuming. The Motor Unit Number Index (MUNIX) is a novel technique based on surface-EMG recordings and requires only 3-5 minutes per muscle. The objective was to explore the feasibility of longitudinal MUNIX measurements in ALS patients. In seven patients enrolled in a clinical trial, eight muscles were studied every 2 months for up to 15 months in addition to the revised ALS-functional rating scale, slow vital capacity, and compound muscle action potentials. The method was well tolerated and easy to perform. Initial MUNIX measures were significantly reduced compared to controls (487 +/- 194 vs. 1459 +/- 113; P < 0.001). Relative drop from baseline paralleled the clinical course and was greater than the drop of other markers of disease progression. MUNIX measurements in multiple muscles are suitable for serial neurophysiologic investigations in ALS. Further longitudinal data are needed for reliability validation.

MUNIX and incremental stimulation MUNE in ALS patients and control subjects

“…Our findings, based on two time points for each patient, showed decline in CMAP and MUNIX, but not a significant decline in IS-MUNE. MUNIX, expressed as percent change from baseline, declined in average by 7.48% (SEM 2.25) per month, in accordance with previously reported range of 2.75-10% per month (Ahn et al, 2010;Nandedkar et al, 2010;Neuwirth et al, 2010). The absence of significant reduction in IS-MUNE may be due to its large variance between subjects and low reproducibility (high MPD) which increases the likelihood that the subjects ranking order would change by the second measurement.…”

MUNIX: Reproducibility and clinical correlations in Amyotrophic Lateral Sclerosis

“…Prospective studies showed a progressive decrease in MUNIX values in small groups of ALS patients, indicating a decrease in the motor unit population Neuwirth et al, 2010). Furtula et al demonstrated that the progressive reduction in MUNIX was comparable to the reduction of incremental stimulation MUNE (IS-MUNE) in a prospective study assessing the ADM muscle in 13 patients with ALS [Furtula et al, 2013].…”

Clinical Measures of Disease Progression in Amyotrophic Lateral Sclerosis

“…However, there are considerable CMAP data as a CMAP is needed in order to calculate the MUNE. And, in fact, the median and ulnar CMAPs actually show substantial decline over time in most patients with ALS, as demonstrated by 2 recent MUNEfocused studies [46,47]. The biggest challenge to the CMAP is its reliability, which is sensitively dependent on electrode positioning, limb and hand positioning, and temperature.…”