Origin of Fasciculations in Amyotrophic Lateral Sclerosis and Benign Fasciculation Syndrome

Fasciculation potentials (FPs) may arise proximally or distally within the peripheral nervous system. We recorded FPs in the tibialis anterior using 2 concentric needle electrodes, ensuring by slight voluntary contraction and electrical nerve stimulation that each electrode recorded motor unit potentials innervated by different axons.Time-locked FPs recorded from both electrodes, suggesting a spinal origin, were most frequent in benign fasciculation syndrome (44%) (P < .001) and amyotrophic lateral sclerosis without reinnervation (27%). Fewer time-locked FPs were found (14%) in the reinnervated tibialis anterior in amyotrophic lateral sclerosis (P < .001).We conclude that in chronic partial denervation FPs are more likely to arise distally and that FPs in benign fasciculation syndrome more frequently arise proximally.