Dynamic analysis of muscles and the internal structure of the peripheral nerve as biomarkers of amyotrophic lateral sclerosis: a pilot study with ultrasound imaging

Introduction: The aim of this study was to determine the behaviour of ultrasound biomarkers of fascicle density and muscle strength in patients with amyotrophic lateral sclerosis (ALS). Methods: We conducted an observational, cross-sectional pilot study of 14 patients with ALS (28.6% women) and 14 controls. Bilateral cross-sectional ultrasound scans were performed in the abductor pollicis brevis (APB) and tibialis anterior (TA) muscles, with recording of muscle thickness (MT) at rest and in contraction, and the difference in thickness. In the median, sciatic, and common peroneal nerves, we analysed the cross-sectional area (CSA), number of fascicles (NF) and fascicle density (FD). Analyses were nested by laterality. Results: Intra- and interrater agreement regarding NF was very good, with a minimum detectable error of < 0.7%. In patients with ALS, MT was lower in the APB both at rest (P = .003; g-Hedges = 1.03) and in contraction (P = .017; g-Hedges = 0.78) and in TA at rest (P = .002; g-Hedges = 0.15) and in contraction (P = .001; g-Hedges = 0.46), with lower thickening capacity. In the nerves, patients displayed lower CSA, with lower NF and higher FD. Significant correlations were found between MT of the ABP and Medical Research Council (MRC) scores for muscle strength (r = 0.34; r(2) = 12%; P = .011) and with revised ALS Functional Rating Scale scores (r = 0.44; r(2) = 19%; P < .001). The difference in TA thickening correlated with MRC scores (r = 0.30; r(2) = 15%; P = .003) and with revised ALS Functional Rating Scale scores (r = 0.26; r(2) = 7%; P = .049). NF in the sciatic nerve showed a significant correlation with MRC scores (r = 0.35; r(2) = 12%; P = .008). Conclusion: MT measurements derived from dynamic testing together with NF and FD may be useful biomarkers for monitoring patients with ALS and establishing a prognosis.