Muscle-nerve ephaptic excitation in some repetitive after-discharges

We describe high frequency muscular repetitive after-discharges (MRDs), induced by maximal or near maximal electrical nerve stimulation, in 5 patients suffering from different peripheral neuropathies. No MRDs were observed at rest or during voluntary contraction. In all the MRDs the interval between the onset of the M wave and the onset of the MRD did not change in relation to the nerve stimulation point; double supramaximal stimulation with adequate delay, delivered at the same nerve site, could suppress the MRDs. From the electrophysiological features the authors suggest an interpretative model: the muscular electric field of the M wave could reexcite ephaptically an intramuscular axon, with defective repolarizing capacity, producing a muscle-nerve reverberating loop.