Primary Position Upbeat Nystagmus

Abstract

Primary position upbeat nystagmus has been associated with lesions of the midbrain, midline cerebellum, and lower brainstem. However, the precise localization still remains unclear. We report one case of primary position upbeat nystagmus in which magnetic resonance imaging (MRI) showed probable lesions of both prepositus hypoglossal nuclei. Morphological and physiological studies have shown that these nuclei play an important role in vertical eye movements. We conclude that the bilateral dysfunction of prepositus hypoglossal nuclei cause the upbeat nystagmus in our patient. © 1992, The Society of Practical Otolaryngology. All rights reserved.