The topographic diagnosis of acquired nystagmus in brainstem disorders

Evidence is presented for a clinical classification of central vestibular syndromes according to the three major planes of action of the vestibulo-ocular reflex (VOR): yaw, pitch, and roll. The plane-specific vestibular syndromes are determined by ocular motor, postural, and perceptual signs. Yaw plane signs are horizontal nystagmus, horizontal past pointing, rotational and lateral body falls to the right or to the left, and horizontal deviation of perceived straight-ahead. Pitch plane signs are upbeat/downbeat nystagmus, forward/backward tilts and falls, and upward or downward deviations of the perceived horizontal. Roll plane signs are torsional nystagmus, skew deviation, ocular torsion, tilts of head, body, and perceived subjective visual vertical. The VOR syndromes defined in this way allow a precise topographic analysis of brainstem lesions according to their level and side. The lesional sites of yaw syndromes are restricted to the pontomedullary level (vestibular nucleus). A tone imbalance in pitch indicates bilateral (paramedian) lesions of the medullary or pontomesencephalic brainstem or bilateral dysfunction of the flocculus. A tone imbalance in roll indicates unilateral lesions, ipsiversive at the pontomedullary level (vestibular nuclei) and contraversive at the pontomesencephalic level (MLF and INC). A unilateral lesion (or stimulation) of the graviceptive pathways, which transduce input from vertical semicircular canals and otolith, affects function in roll, whereas bilateral lesions affect function in pitch.