The origin of spontaneous discharges in acquired neuromyotonia. A Macro EMG study

Objective To study the generator sites of spontaneous discharges in patients with immune-mediated neuromyotonia. Methods Macro EMGs triggered by both spontaneously and voluntarily activated single action potentials were recorded and the mean peak-to-peak amplitude and area of the macro motor unit potentials were compared in two patients with typical acquired neuromyotonia having positive antibodies against voltage-gated potassium channels. Results Mean peak-to-peak amplitude and area of Macro EMG motor unit potentials (macro MUPs) triggered by spontaneous discharges were significantly smaller than those triggered by voluntary activation in both patients. However, a few macro MUPs triggered by spontaneous discharges resembled those triggered by voluntary activation. Conclusions Spontaneous discharges in two patients with immune-mediated neuromyotonia seem to be mostly generated at sites distal to the terminal axon branching points. Significance This finding may provide a new insight in the understanding of spontaneous discharges in immune-mediated neuromyotonia.