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.