Evaluation of F wave and split hand index in patients with amyotrophic lateral sclerosis

Abstract

Abstract Background Amyotrophic lateral sclerosis (ALS) is characterized by gradual disturbance of both upper and lower motor neurons (LMN). In ALS, muscle wasting favors the abductor pollicis brevis (APB) and first dorsal interosseous (FDI), with relative preservation of abductor digiti minimi (ADM). Objectives To interpret F wave changes in the context of upper and LMN dysfunction and the differences in dysfunction between spinal motoneurons innervating the APB and ADM. Patients and methods Forty-four subjects were studied (22 patients with ALS and 22 controls). F wave was elicited by 50 electrical stimuli from the median and ulnar nerves, and the split hand index (SHI) was measured. Results F latency mean, median, and maximum and F amplitude mean, median, and maximum F/M amplitude ratio were increased in patients with versus those without pyramidal signs. Limb-onset ALS patients showed the biggest reduction in SHI. The APB muscle of patients with no detectable wasting and upper MN (UMN) signs showed reduced F wave persistence, mean F wave latency and amplitudes, increased index repeater neuron and index F repeater, and mean F/M amplitude ratio. Conclusion There is enhanced segmental motoneuronal excitability following UMN dysfunctions. SHI appears to be a diagnostic biomarker for ALS. Abnormal F parameters recorded from APB muscle can distinct patients with ALS from the normal controls to a greater extent than do the APB/ADM and FDI/ADM compound muscle action potential amplitude ratios.

Keywords

• ALS
• F wave
• Split hand index