Perverted Downward Corrective Saccades During Horizontal Head Impulses in Chiari Malformation
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The mechanism of perverted vertical responses during horizontal head impulse tests (HITs) requires further elucidation. A 47-year-old woman with a Chiari malformation showed alternating skew deviation, downbeat nystagmus with an increasing slow phase velocity, impaired smooth pursuit, and upward ocular deviation during horizontal HITs and corrective downward saccades in the presence of normal bithermal caloric tests and intact tilt suppressions of the post-rotatory nystagmus. These findings suggest dysfunction of the inferior cerebellum including the tonsil, nodulus, and uvula. We propose that disruption of signals from the medial part of the vestibulocerebellum, which normally inhibits the lateral and anterior canal pathways, may elicit an upward misdirection of the eye velocity during rapid horizontal head rotation. Otherwise, the Chiari malformation may have directly affected the brainstem structures involved in the direction matrix of the vestibulo-ocular reflex.
KeywordsChiari malformation Head impulse test Downbeat nystagmus
S.-H. K., as the first author, designed the study, interpreted and analyzed the data, and drafted the manuscript. H. J. K. acquired the data and made revisions of the manuscript and figures. J.-S. K., as the corresponding author, designed the study, interpreted the data, and made critical revisions of the manuscript.
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF-2016R1D1A1B04935568).
Compliance with Ethical Standards
S.-H. K and H-J. K report no disclosure.
J.-S. K. serves as an associate editor of Frontiers in Neuro-otology and on the Editorial Boards of the Journal of Clinical Neurology, Frontiers in Neuro-ophthalmology, Journal of Neuro-ophthalmology, Journal of Vestibular Research, and Journal of Neurology and Medicine.
Conflict of Interest
The authors declare that they have no conflict of interest.