MUNIX: Reproducibility and clinical correlations in Amyotrophic Lateral Sclerosis

Abstract Objective To study the reproducibility, diagnostic yield to detect denervation, and clinical correlations of the Motor Unit Number Index (MUNIX) in subjects with Amyotrophic Lateral Sclerosis (ALS). Methods MUNIX evaluation was performed in three muscles twice on the same day to assess reproducibility. Cut-off values for the MUNIX were based on data from 51 healthy subjects (controls) to evaluate the sensitivity of the technique to detect denervation in 30 subjects with ALS. Results The method had good reproducibility. The variability was greater in the ALS group. In 23 ALS subjects (77%), low MUNIX values were detected. Most of the muscles with low MUNIX had also low compound muscle action potential (CMAP) and strength, but these parameters were normal in 9% of muscles. According to ROC curve analysis, MUNIX was generally accurate (AUC = 0.9504) for discriminating between healthy individuals and subjects with at least one denervated muscle. Conclusions MUNIX variability was higher in the ALS group. The method showed good diagnostic performance for the detection of denervation in a sample of patients with ALS. Significance This study demonstrated that in addition to being a quantitative tool MUNIX can detect denervation in subjects with ALS.