Prevalence of denervation in paraspinal and foot intrinsic musculature

Objective: The primary purpose of this investigation was to determine the p revalence of abnormal spontaneous activity (positive sharp waves (PSWs) and fibrillation potentials (FPs)) in selected lumbosacral paraspinal and foot intrinsic muscles in an asymptomatic healthy population. Design: This was a prospective assessment of 50 individuals without history or physical findings suggestive of peripheral neuromuscular disease whereb y a monopolar needle electrode was located in the unilateral L4 and L5 para spinal as well as abductor hallucis and extensor digitorum brevis muscles. These muscles were extensively evaluated for the presence of PSWs, FPs, and fasciculation potentials. Results: Ten subjects per decade from 20-59 yr and ten subjects from 60-80 yr comprised the 50 participants (28 women), resulting in a mean age of 45 +/- 15.9 (range, 20-76) yr. A single individual (prevalence, 2%) demonstrat ed fibrillation potentials in the extensor digitorum brevis, and FPs and PS Ws were detected in two subjects' (4% prevalence) L4/L5 paraspinal muscles. Ninety-four percent of the subjects had fasciculation potentials in the ab ductor hallucis, whereas 60% had these waveforms in the extensor digitorum brevis, Only 6% of subjects had fasciculation potentials in the L4 but not L5 paraspinal muscles. All subjects demonstrated both prototypical and "aty pical" appearing endplate spikes in all of the muscles examined. Conclusions: We failed to confirm the previously reported prevalence of FPs and PSWs in both the paraspinal and foot intrinsic musculature. Atypical a ppearing endplate spikes, however, display configurations similar to FPs an d PSWs and were present in all subjects. Failure to pay close attention to the discharge rate and rhythm of endplate spikes can lead to misinterpretin g these waveforms as FPs and PSWs, It is likely that the previously reporte d high prevalence of spontaneous activity In healthy persons resulted from not fully appreciating the similarity between innervated and denervated spo ntaneous single muscle fiber discharge configurations.