Fasciculations and their F-response revisited: High-density surface EMG in ALS and benign fasciculations

ObjectiveTo compare the prevalence of fasciculation potentials (FPs) with F-responses between patients with amyotrophic lateral sclerosis (ALS) and patients with benign fasciculations.MethodsIn seven patients with ALS and seven patients with benign fasciculations, high-density surface EMG was recorded for 15 min from the gastrocnemius muscle. Template matching was used to search for pairs of FPs with a repetition within 10–110 ms.ResultsInterspike interval (ISI) histograms were constructed from 282 pairs of benign fasciculations and from 337 FP pairs in ALS. Peaks attributable to F-waves were found at latencies of 32 ms (benign) and 35 ms (ALS). Five patients with benign fasciculations and four patients with ALS had FPs with F-waves.ConclusionsF-waves of FPs occur in both conditions – therefore they are not diagnostically helpful.SignificanceF-waves confirm the distal origin of FPs for an individual axon. The occurrence of these FPs in a benign condition suggests that the generation of ectopic discharges in the distal axons is not specific to progressive neurodegeneration.

► High-density surface EMG is a powerful method to record the firing patterns of multiple fasciculation potentials.
► Both in patients with ALS and in patients with benign fasciculations, fasciculation potentials with F-waves are found.
► The distal origin of fasciculations is not related to denervation and fasciculations with F-waves are not diagnostically relevant.