Walsh & Hoyt: Nystagmus Caused by Peripheral Vestibular Imbalance

Nystagmus related to imbalance in the vestibular pathway can be caused by damage to peripheral or central structures. Because the nystagmus varies, it usually is possible to distinguish nystagmus caused by peripheral vestibular imbalance from nystagmus caused by central vestibular imbalance. Disease affecting the peripheral vestibular pathway (i.e., the labyrinth, vestibular nerve, and its root entry zone) causes nystagmus with linear slow phases. Such unidirectional slow-phase drifts reflect an imbalance in the level of tonic neural activity in the vestibular nuclei. If disease leads to reduced activity, for example, in the vestibular nuclei on the left side, then the vestibular nuclei on the right side will drive the eyes in a slow phase to the left. In this example, quick phases will be directed to the right away from the side of the lesion. Paradoxically, some patients show nystagmus with a horizontal component that beats toward the side of the lesion. Such cases may be ""recovery nystagmus,"" which represents the effects of a central adaptation process. An imbalance of vestibular tone usually also causes vertigo and a tendency to fall toward the side of the lesion. Apart from these attendant symptoms, two features of the nystagmus itself are useful in identifying the vestibular periphery as the culprit: its trajectory (direction) and whether it is suppressed by visual fixation