Aperiodic alternating nystagmus in acute lateral medullary infarction: a video report
Article information
An 81-year-old man presented with acute vertigo, left tilt, and headache for 1 day. Neurologic examination revealed spontaneous waxing and waning nystagmus with horizontal directional changes with omnidirectional gaze-evoked nystagmus and vigorous left-beating nystagmus on the head-shaking test. Diffusion-weighted magnetic resonance imaging demonstrated an acute infarction involving the left lateral medulla (Fig. 1A). Videooculography showed aperiodic alternating nystagmus (aPAN) with an irregular interval (Supplementary Video 1, Fig. 1B). Spontaneous right-beating nystagmus (peak slow-phase velocity, 10.4°/sec) lasted 104 seconds and gradually decreased. The nystagmus then changed direction to the left and lasted for 134 seconds (peak slow-phase velocity, 7.9°/sec) before reversing to the right again. Written informed consent was obtained for publication of this case report and accompanying images.

Brain magnetic resonance imaging demonstrated high signal intensity (arrow) in the left lateral medulla on the diffusion-weighted image (A). The plotting of the nystagmus reveals a spontaneous right-beating nystagmus (peak slow-phase velocity, 10.4°/sec) that reverses to left-beating nystagmus (peak slow-phase velocity, 7.9°/sec) and then reversing back to the right. A negative value indicates a rightward direction of the slow components of nystagmus (B).
aPAN, which exhibits spontaneous alternating nystagmus without periodicity and regularity, is rarely seen in association with various peripheral and central vestibular disorders [1-3]. In lateral medullary stroke, aPAN may be caused by impairment of velocity storage and gaze holding [2].
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Funding/Support
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Conflicts of Interest
Ji-Yun Park is the Editor-in-Chief of Research in Vestibular Science and was not involved in the review process of this article. All authors have no other conflicts of interest to declare.
Availability of Data and Materials
All data generated or analyzed during this study are included in this published article. For other data, these may be requested through the corresponding author.
SUPPLEMENTARY MATERIALS
Supplementary materials can be found via https://doi.org/10.21790/rvs.2024.010.
Supplementary Video 1.
Videooculography showed aperiodic alternating nystagmus with an irregular interval. Initially, spontaneous right-beating nystagmus (peak slow-phase velocity, 10.4°/sec) lasted 104 seconds and gradually decreased. The nystagmus then switched direction to the left and lasted for 134 seconds (peak slow-phase velocity, 7.9°/sec) before reversing back to the right again.