Afterdischarge activity in neuropathic patients with frequent muscle cramps

Objectives - To evaluate the presence of the afterdischarge activity following M- and F-waves in patients with peripheral neuropathies with or without muscle cramps. Material and methods - Ten patients with peripheral neuropathies complaining of frequent muscle leg cramps (Group 1) and 14 patients with peripheral neuropathies without muscle cramps (Group 2) participated in our study. The afterdischarge was evaluated through a repetitive stimulation of the peroneal and tibial nerves. Results - An abnormal afterdischarge activity following F-wave was identified below 5 Hz only in Group 1. On high frequency of stimulation (> 5 Hz), this activity was present in every patient in Group 1. Moreover, it was particularly present in the muscle affected by cramps. Conclusion - Since the afterdischarges following F-waves have been considered to be the result of a hyperactive 'bistable' state of alfa-motor neurons, our findings are indicative of an impairment of motor neuron excitability. Thus, it is hypothesizable that either peripheral and central mechanisms may together contribute in producing muscle cramps.