VESTIBULAR NEURITIS SPARES THE INFERIOR DIVISION OF THE VESTIBULAR NERVE

Acute unilateral vestibulopathy, or vestibular neuritis, is the second most common cause of vertigo. To quantify the involvement of the diff erent semicircular canal (SCC) afferents in this disease, we studied r ite three-dimensional (3D) properties of the vestibuloocular reflex (V OR) in 16 patients 3-10 days after onset of symptoms. Using 3D magneti c search coil eye movement recordings, we measured the speed and axis of eye rotation during spontaneous nystagmus and during rotation in ri te planes of the different SCCs. In all patients, spontaneous nystagmu s axes clustered between the direction expected with involvement of ju st one horizontal SCC and the direction expected with combined involve ment of the horizontal and anterior SCC on one side. Likewise, dynamic asymmetries were found only, during rotations about axes which stimul ated the ipsilesional horizontal or ipsilesional anterior SCCs. No asy mmetry was found when the ipsilesional posterior SCC was stimulated. T hus, both measurements a complete unilateral vestibular lesion and tha t this partial lesion affects the superior division of the vestibular nerve which includes the afferents from the horizontal and anterior SC Cs.