Clinical Utility of Far-Field Potentials in Amyotrophic Lateral Sclerosis.

Abstract

Introduction/aims: Far field potentials (FFP) have been proposed as a reliable neurophysiological prognostic biomarker in amyotrophic lateral sclerosis (ALS). This study evaluates the diagnostic utility of ulnar nerve FFP in ALS.

Methods: Comprehensive peripheral neurophysiological assessments were conducted in 62 ALS and 43 ALS-mimicking disorder participants. The ulnar nerve was stimulated at the wrist, recording motor responses over the abductor digit minimi (ADM) muscle. Conventional compound muscle action potentials (CMAP), FFP, and near field potential amplitudes were recorded, alongside the split-hand index, neurophysiological index, motor unit number estimation (MScanFit-MUNE), and motor unit index (MUNIX). Diagnostic utility was evaluated using receiver operating characteristic (ROC) analysis.

Results: In ALS, FFP amplitude was significantly lower (5.07 ± 0.36 mV) compared to ALS mimics (8.25 ± 0.40 mV, p < 0.001). FFP amplitude exhibited a moderate-to-strong correlation with neurophysiological biomarkers, including CMAP amplitude (ρ = 0.77, p < 0.001), split-hand index (ρ = 0.53, p < 0.001), neurophysiological index (ρ = 0.52, p < 0.001), MUNIX (ρ = 0.69, p < 0.001), and MScanFit-MUNE (ρ = 0.66, p < 0.001). Weak-to-moderate correlations were also observed with clinical measures of disease progression, including upper limb muscle strength, ALS functional rating score-revised (ALSFRS-R) and the rate of decline in the ALSFRS-R fine motor subscore. ROC analysis demonstrated that FFP amplitude reliably distinguished ALS from mimicking disorders (AUC = 0.80, 95% CI: 0.71-0.89), with consistent diagnostic accuracy across ALS phenotypes.

Discussion: The diagnostic capability of FFP amplitude was comparable to established neurophysiological biomarkers utilized in ALS. It is a promising prognostic and diagnostic biomarker for ALS. Its simplicity and reproducibility complement traditional neurophysiological measures, offering potential for clinical application in ALS diagnosis and monitoring.