When Dizziness Masks Brain Inflammation: Rare Cerebellitis Case Reveals Telltale Eye-Movement Clues

A case of acute cerebellitis, an inflammatory condition of the cerebellum that usually announces itself with unsteady gait, slurred speech, and incoordination, has provided neurologists with an unusually detailed look at what happens when the brain’s balance organ is suddenly silenced. In a letter to the editors published in the Journal of Neurology, a team led by Hyesoo Kwon of Keimyung University Dongsan Hospital in Daegu, South Korea, together with Hae Won Kim and Hyun Ah Kim, describes a patient whose illness presented almost entirely with vestibular symptoms, the disorienting sensations of dizziness and imbalance that most clinicians would first attribute to the inner ear rather than to the brain.

The cerebellum, tucked beneath the rear of the skull, is best known for fine-tuning movement. But a substantial portion of it, the vestibulocerebellum, is devoted to calibrating the vestibulo-ocular reflex, or VOR, the automatic eye movement that keeps images stable on the retina when the head moves. When this calibration fails, patients experience the world as a blur of motion and feel profoundly unsteady. The Korean team’s report shows that when inflammation strikes this region, the resulting eye-movement abnormalities can be so distinctive that they point directly to cerebellar disinhibition, the loss of the cerebellum’s normal restraining influence on vestibular circuits.

The most striking finding in the case involves what the authors call reversed corrective saccades. During the head impulse test, a bedside maneuver in which the examiner turns the patient’s head rapidly and unexpectedly while the patient fixes their gaze on a target, a healthy vestibular system generates a compensatory eye movement that keeps the eyes locked on the target. If the reflex is weak, the eyes are dragged off target with the head, and the patient makes a quick corrective saccade back to the target. In cerebellar disease, however, the corrective movement can go the wrong way, jumping in the same direction as the head turn rather than back toward the target. This paradoxical sign, previously documented in acute cerebellar dysfunction by Choi and colleagues in a 2014 study, indicates that the inhibitory brake normally applied by the cerebellum has been released, allowing the vestibular response to overshoot rather than undershoot.

Equally revealing was the frequency-dependent behavior of the vestibulo-ocular reflex. The team observed VOR hyperactivity that varied with the frequency of head rotation, a pattern that helps localize the problem to specific cerebellar structures. The nodulus and uvula, midline structures of the vestibulocerebellum, are known from decades of experimental work, including classic studies by Cohen and colleagues published in 2002, to control the spatial orientation of the angular vestibulo-ocular reflex and to regulate the velocity storage mechanism, a central process that prolongs and shapes vestibular signals. The flocculus, by contrast, exerts direct inhibitory control over the VOR gain itself. When the flocculus is damaged, as Yacovino and colleagues described in isolated floccular infarction, the VOR gain rises, producing hyperactive eye responses and oscillopsia, the distressing sensation that the visual world is jumping.

Acute cerebellitis is an uncommon diagnosis, and its presentation in adults is rarer still. Most of the literature concerns children, in whom the condition frequently follows viral infections or arises with autoimmune antibodies against neural targets. A large Italian multicenter retrospective study published in 2017 by Lancella and colleagues documented the pediatric experience over eleven years, while a 2023 European study by Quack and colleagues systematically examined autoantibody status, neuroradiological findings, and clinical features in children with the condition. In adults, reports are largely confined to individual case descriptions, such as the review by Van Samkar and colleagues published in BMC Research Notes in 2017. The scarcity of adult cases means that each well-documented patient adds meaningful weight to the clinical map of the disease.

What makes this case particularly instructive is the predominance of vestibular symptoms. A patient who complains primarily of dizziness and imbalance is far more likely to be evaluated for benign paroxysmal positional vertigo, vestibular neuritis, or other inner ear disorders than for brain inflammation. Yet the eye-movement examination, performed with modern video head impulse testing, can separate these possibilities with remarkable precision. Video head impulse testing has become a cornerstone of the assessment of central vestibular disorders, as summarized by Choi, Kim, and Kim in a 2018 review in Neurology, because it measures the gain of the vestibulo-ocular reflex across individual semicircular canals and captures the corrective saccades that reveal where in the vestibular pathway the fault lies.

The frequency dependence of the VOR abnormality carries specific mechanistic significance. The vestibulo-ocular reflex operates across a range of head movement frequencies, from slow postural sway to rapid voluntary head turns. Different cerebellar regions modulate the reflex at different points along this spectrum. Studies of patients with chronic degeneration of the vestibulocerebellum by Bertolini and colleagues suggested that vestibular self-motion perception is shaped by the velocity storage mechanism, and work by Lee and colleagues on spinocerebellar ataxia type 6 traced how vestibular function evolves during head impulses in a degenerative disease. Against this background, the acute, frequency-dependent hyperactivity seen in the present case of cerebellitis stands out as a signature of sudden disinhibition rather than gradual degeneration, offering a dynamic window into cerebellar physiology that chronic conditions cannot provide.

The concept of cerebellar disinhibition unifies the two key signs in the case. Under normal conditions, the vestibulocerebellum continuously calibrates the vestibulo-ocular reflex, comparing the expected sensory consequences of a head movement with the actual signals arriving from the labyrinth and adjusting the reflex gain accordingly. This internal model computation, as Cullen described in a 2023 review in Trends in Neurosciences, is one of the cerebellum’s central contributions to the perception of self-motion. When inflammation disables this computation, the inhibitory control is lost, the reflex gain climbs above normal, and corrective saccades reverse direction because the eyes have overshot rather than undershot the target. The same logic explains other cerebellar eye signs, such as vibration-induced downbeat nystagmus, which Kim and colleagues reported in 2023 as a new cerebellar sign observed in a paraneoplastic syndrome.

For clinicians, the practical lesson is that a predominantly vestibular presentation does not exclude cerebellar inflammation. The authors emphasize that reversed corrective saccades during head impulse testing and frequency-dependent VOR hyperactivity should be recognized as clues to cerebellar disinhibition, prompting appropriate neuroimaging and further workup rather than discharge with a diagnosis of uncomplicated inner ear disease. The case was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of Keimyung University Dongsan Hospital, with written informed consent obtained from the patient’s parent for publication of the report and accompanying images. The authors report no conflicts of interest, and the work received no dedicated funding.

Beyond its immediate clinical message, the report illustrates how a single carefully examined patient can sharpen our understanding of a brain region that remains incompletely mapped. The cerebellum’s role in vestibular processing has been built up over decades through lesion studies, animal experiments, and increasingly sophisticated bedside testing, and acute, reversible insults such as cerebellitis offer some of the cleanest natural experiments available. As video head impulse testing and related technologies spread through emergency departments and vestibular clinics, signs that were once obscure, such as reversed corrective saccades, are likely to be recognized more often, turning a rare case report into a practical diagnostic lesson for the many patients who arrive complaining simply that the room will not stop spinning.

Subject of Research: Acute cerebellitis presenting with vestibular symptoms and distinctive eye-movement signs of cerebellar disinhibition

Article Title: Acute cerebellitis presenting predominantly with vestibular symptoms: reversed corrective saccades and frequency-dependent VOR hyperactivity as clues to cerebellar disinhibition

Article References: Acute cerebellitis presenting predominantly with vestibular symptoms: reversed corrective saccades and frequency-dependent VOR hyperactivity as clues to cerebellar disinhibition. (n.d.). https://doi.org/10.1007/s00415-026-14204-2

Image Credits: AI Generated

DOI: 10.1007/s00415-026-14204-2

Keywords: acute cerebellitis, vestibular symptoms, vestibulo-ocular reflex, reversed corrective saccades, head impulse test, cerebellar disinhibition, vestibulocerebellum, flocculus, nodulus, dizziness, neuro-otology, Journal of Neurology