Usefulness of Nystagmus Patterns in Distinguishing Peripheral From Central Acute Vestibular Syndromes at the Bedside: A Critical Review.

Vertigo and dizziness are amongst the most frequent presenting symptoms in the emergency room, accounting for up to 4% of all emergency consultations. The broadness of their differential diagnosis and the often transient nature of these symptoms pose a significant challenge to the treating physician. Combining various subtle oculomotor signs at the bedside has been very successful in distinguishing peripheral from central causes in acutely dizzy patients meeting diagnostic criteria for the acute vestibular syndrome (i.e., acute and prolonged vertigo or dizziness accompanied by nausea or vomiting, gait imbalance, motion intolerance, and [not mandatory] nystagmus). While the diagnostic accuracy of the HINTS (Head-Impulse-Nystagmus-Test-of-Skew) algorithm has been studied extensively, less is known about the value of various nystagmus patterns seen at the bedside in patients with an acute vestibular syndrome. Here we review both spontaneous and triggered presenting nystagmus patterns and discuss their impacts and limitations, including primary-gaze horizontal, vertical, and torsional nystagmus, nystagmus during eccentric gaze, and nystagmus triggered by stimuli such as head-shaking, hyperventilation, positional testing, vibration, and the Valsalva maneuver. We conclude that the usefulness of nystagmus patterns in discriminating peripheral and central causes strongly depends on the pattern seen and the type of testing performed, being highly predictive of a central cause for torsional and vertical spontaneous nystagmus, downbeat, or apogeotropic horizontal and treatment-refractory positional nystagmus. The predictive value for central causes was moderate only for vertical nystagmus after horizontal head-shaking ("perverted" head-shaking nystagmus) since it can also occur in peripheral cases, while the predictive value was low for vibration-induced nystagmus and Valsalva-induced nystagmus.