Video 6.7 Head-shaking-induced nystagmus in a patient with previous vestibular neuritis from Neuro-Ophthalmology and Neuro-Otology Textbook

: This is a 50-year-old man who experienced the abrupt onset of imbalance, dizziness and left-sided hearing loss 4 months prior to this examination. He was found to have herpetic vesicles in the left external auditory canal and diagnosed with Ramsay Hunt syndrome. On exam (4 months after the onset), there was an abnormal head impulse test (HIT) to the left side, and with fixation-removed, there was very mild right-beating nystagmus. However, following 15 seconds of 2-3 Hz horizontal head-shaking, there was robust right-beating nystagmus. Video HIT showed left sided vestibular loss with low gains (<0.7 - gain is calculated with this system as the area under the eye movement velocity curve/area under the head movement velocity curve) and corrective saccades in the planes of the horizontal, anterior and posterior canals, which is commonly seen with Ramsay Hunt syndrome. Ewald's second law states that ampullopetal endolymph flow will cause greater stimulation than ampullofugal flow within the horizontal canals. Head-shaking, therefore, leads to transiently asymmetric vestibular afferents when unilateral vestibular loss is present, leading to a contralesional post-head-shake nystagmus as in this patient. Head-shaking is one of several provocative maneuvers that can bring out a patient's underlying vestibular asymmetry months or even years after the insult occurs (vibration and hyperventilation are others). - - : This patient experienced the abrupt onset of imbalance, dizziness and left-sided hearing loss 4 months prior to this examination. He was found to have herpetic vesicles in the left external auditory canal and diagnosed with Ramsay Hunt syndrome. On exam (4 months after the onset), there was an abnormal head impulse test (HIT) to the left side, and with fixation-removed, there was very mild right-beating nystagmus. However, following 15 seconds of 2-3 Hz horizontal head-shaking, there was robust right-beating nystagmus. Video HIT showed left-sided vestibular loss with low gains (