Spontaneous continuous motor unit single discharges

Introduction Motor unit hyperexcitability (MUH) may become manifest in needle electromyography (EMG) recordings as fasciculation potentials, myokymic discharges, or neuromyotonic discharges. Here, we describe a further MUH phenomenon. Methods Needle EMG recordings of the Neurology Hospital of Halle (Saale) stored in a video mode as .wav data between 2000 and 2015 were screened for spontaneous continuous motor unit single discharges (SCMUSD). Results We identified 23 video needle EMG waveforms from 14 patients with SCMUSD. The corresponding motor units discharged at a rate of about 6 H Z (6.3 +/- 4.0; range, 1.3-18.1). The coefficient of variation of the discharge rate was 3.5% +/- 1.7%. Neurogenic disorders were diagnosed in 12 patients, limb girdle muscle dystrophy was diagnosed in one patient, and stiff-limb syndrome was diagnosed in one patient. Discussion Spontaneous continuous motor unit single discharge, as described here, widens the spectrum of MUH phenomena.