Vibration-induced nystagmus in a patient with vestibular neuritis

This is a 60-year-old man who experienced the sudden onset of vertigo, oscillopsia, imbalance, nausea and vomiting. He was seen in the emergency department within hours and had spontaneous right-beating (RBN) and torsional (top poles toward right ear) nystagmus that was unidirectional in all directions of gaze; an abnormal head impulse test to the left side (a corrective saccade with head impulses to the left); and a negative test of skew (no vertical refixation movement with alternate cover testing); and there was no unilateral hearing loss. Taken together, his exam suggested a peripheral (benign) pattern of the HINTS ‘Plus' exam (Head Impulse, Nystagmus, Test of Skew, where ‘Plus' refers to whether hearing loss is present), and a diagnosis of left vestibular neuritis was made. One week later, the patient was seen as an outpatient. The spontaneous RBN was much less prominent and the patient was much less symptomatic. A video head impulse test (vHIT) was performed, which demonstrated the corrective saccades seen at the bedside, as well as a gain asymmetry between the impaired (left) and normal (right) sides. It was felt that the gain was >1 to the right mainly due to goggle slippage during the vHIT. This may have increased the gain on the impaired side as well. With horizontal head-shaking and vibration, the baseline RBN increased substantially. Seen in the video is the vibration-induced RBN. Skull vibration induces nystagmus with unilateral vestibular loss (slow phase toward the paretic ear) that is time-locked to the vibratory stimulation. It also beats in the same direction regardless of whether the right or left mastoid is stimulated, or whether the vibrator is placed over the vertex1. This is because the stimulus is effectively transmitted to both labyrinths. Since vibration is a stimulus that excites semicircular neurons, when vestibular asymmetry exists (e.g., left peripheral vestibulopathy due to vestibular neuritis), the unaffected (right) side will be activated normally while the affected (left) side will not. This will create a slow phase drift toward the paretic ear as in this patient with a contralesional nystagmus(1).1. Dumas G, Curthoys IS, Lion A, Perrin P, Schmerber S. The Skull Vibration-Induced Nystagmus Test of Vestibular Function-A Review. Front Neurol 2017;8:41