Central vestibular disorders.

Dizziness or vertigo is an erroneous perception of selfmotion or object-motion as well as an unpleasant distortion of static gravitational orientation. It is caused by a mismatch between the vestibular, visual, and somatosensory systems. Thanks to their functional overlap, the three systems are able to compensate, in part, for each other's deficiencies. Thus, vertigo is not a well-defined disease entity, but rather a multisensory syndrome that results when there is a pathological dysfunction of any of the stabilizing sensory systems (e.g., central vestibular disorders, peripheral vestibular diseases with asymmetric input into the vestibular nuclei). This article provides an overview of the most important and frequent forms of central vestibular vertigo syndromes, including basilar/vestibular migraine, which are characterized by ocular motor, postural, and perceptual signs. In a simple clinical classification they can be separated according to the three major planes of action of the vestibulo-ocular reflex: yaw, roll, and pitch. A tonic imbalance in yaw is characterized by horizontal nystagmus, lateropulsion of the eyes, past-pointing, rotational and lateral body falls, and lateral deviation of the perceived straight-ahead. A tonic imbalance in roll is defined by torsional nystagmus, skew deviation, ocular torsion, tilts of head, body, and the perceived vertical. Finally, a tonic imbalance in pitch can be characterized by some forms of upbeat or downbeat nystagmus, fore-aft tilts and falls, and vertical deviation of the perceived straight ahead. The thus defined syndromes allow for a precise topographic diagnosis as regards their level and side.