Lack of correlation between spontaneous fasciculations and double discharges of voluntarily activated motor units.

We have studied the possible correlation between spontaneous fasciculations and double discharges or voluntarily activated motor units in myelopathies and other proximal neuropathies. Though both these phenomena are common in these diseases, they seem to have no correlation in individual muscles. It is concluded that spontaneous fasciculations and doubling of voluntarily activated motor unit potentials have different sites of origin or different mechanism. For example, if doubling reflects a disturbance of firing in the axon hillock, spontaneous fasciculations may originate in a more peripheral part of the motor axon.