Reply to the Commentary on Luis et al. "Spontaneous plugging of the horizontal semicircular canal with reversible canal dysfunction and recovery of vestibular evoked myogenic potentials".

OBJECTIVE To evaluate the clinical pathophysiology of oculomotor changes in a patient presenting with a spontaneous semicircular horizontal canal plug. PATIENT A 42-year-old man with acute spontaneous vertigo with spinning and persistent left-horizontal nystagmus, intensity but not direction dependent on head orientation with respect to gravity, indicating a benign paroxysmal positional vertigo due to otoconia causing a plug in the horizontal semicircular canal. INTERVENTION Electrophysiological and video-oculographic testing; vestibular rehabilitation. MAIN OUTCOME MEASURES Cervical and ocular vestibular evoked myogenic potentials (VEMPs); video head impulse testing. RESULTS The video head-impulse test revealed an eye velocity cutoff at 80°/s in the time interval from 40 to 90 ms after initiation of head impulses to the right. This normalized within 2 days after liberatory maneuvers, documenting for the first time a reversible deficiency of the cupular-endolymph high-frequency system dynamics. Cervical and ocular vestibular myogenic potentials were absent during stimulation of the affected side before the liberatory maneuvers but normalized within 30 to 80 days. CONCLUSION This case is special in 4 respects: 1) nystagmus intensity, but not direction, was dependent on head orientation with respect to gravity, indicating a horizontal canal plug; 2) VEMPs were asymmetrical before liberatory maneuvers; 3) VEMPs recovered after Day 30; and 4) video head-impulse test asymmetry recovered. These observations challenge the common belief that VEMPs are evoked by otolith stimulation only. Instead, the assumption of a reversible canal dysfunction by a plug offers a more plausible explanation for all effects.