VESTIBULO-MASSETERIC REFLEX (VMR) AND ACOUSTIC-MASSETERIC REFLEX (AMR): NORMATIVE VALUES

Objective To gain normative values for VMR and AMR, two myogenic potentials recently described in masseter muscles (MM), which normal values for clinical use have not been defined yet. Methods Sixty healthy subjects (aged 13-66 years; 39 females) underwent VMR and AMR recording, during unilateral and bilateral clicks (0.1ms, 143-108dB-SPL, 5Hz), from active MM, through surface electrodes in a belly-to-tendon double montage (active electrode over MM belly, reference over the mandible angle and zygomatic arch). VMR and AMR onset and peak latencies as well as corrected amplitudes (ratio) were calculated in the averaged unrectified-EMG, according to stimulation/recording side, electrode montage and sample demographics. Results VMR and AMR were bilateral and symmetric, with no significant age-related differences. Following bilateral stimulation, onsets were 8.07±0.98ms and 12.06±1.90ms, positive-peaklatencies were 11.2±0.88ms and 15.37±1.10ms, ratios were 0.64±0.28 and 0.51±0.26, respectively. Unilateral stimulation induced responses of similar latency but 30-35% smaller (p<0.001) than bilateral stimulation. The electrode montage with zigomatic reference provided the largest and more consistent responses, with AMR occurring significantly earlier in women than in men (p<0.01). Conclusions and Significance Availability of normative values for VMR and AMR can offer clinicians an additional tool to test brainstem circuits in normal and pathological conditions.