People living with adult-onset cerebellar ataxia (AOCA) often struggle with balance, coordination, and walking. These symptoms are usually blamed on problems in the cerebellum—the part of the brain responsible for coordinating movement. But new research suggests another important piece of the puzzle may be overlooked: the vestibular system, the sensory system in the inner ear that helps us maintain balance and keep our vision steady while moving our heads.
A new study from researchers at the Johns Hopkins Ataxia Center found that more than half of adults with cerebellar ataxia also have measurable vestibular dysfunction. The findings suggest that many people with ataxia could benefit from vestibular testing—and possibly vestibular rehabilitation—to address symptoms that may not be caused by cerebellar disease alone.
What is adult-onset cerebellar ataxia?
Adult-onset cerebellar ataxia refers to a group of neurological disorders that begin in adulthood and gradually affect coordination, balance, speech, and walking. Some forms are inherited, while others have no known genetic cause.
Because the cerebellum helps coordinate movement, damage to this part of the brain can make it difficult to walk steadily or perform precise movements. However, balance depends on much more than the cerebellum. It also relies on healthy input from the eyes, muscles and joints, and the vestibular organs in the inner ear.
When both the cerebellum and the vestibular system are affected, balance problems can become significantly worse.
The vestibulo-ocular reflex: Your body’s built-in image stabilizer
The researchers focused on something called the vestibulo-ocular reflex (VOR).
Simply put, the VOR keeps your vision clear while your head is moving. For example, if you turn your head quickly to look over your shoulder, your eyes automatically move in the opposite direction at exactly the right speed so that the world doesn’t appear to bounce or blur.
When the VOR isn’t working properly, people may experience:
- Blurred or bouncing vision while walking (called oscillopsia)
- Increased imbalance
- Difficulty walking, especially in the dark or on uneven ground
- Greater risk of falls
These symptoms can overlap with those caused by cerebellar disease, making it difficult to recognize that the vestibular system is contributing as well.
How did the researchers study this?
The investigators reviewed the records of 302 adults with cerebellar ataxia who were evaluated at the Johns Hopkins Ataxia Center between 2023 and 2025.
Each participant underwent a video head impulse test (vHIT), a quick, non-invasive test that measures how well the vestibulo-ocular reflex is functioning. During the test, a clinician gently and rapidly turns the patient’s head while specialized goggles record eye movements.
The researchers looked for:
- Vestibular hypofunction – when the vestibular system responds too weakly
- Vestibular hyperfunction – when responses are stronger than expected
- Bilateral vestibulopathy (BVP) – severe loss of vestibular function in both inner ears
What did they find?
The results were striking.
Overall:
- 56% of patients had an abnormal vestibular response.
- 42% had vestibular hypofunction.
- 14% had vestibular hyperfunction.
This means vestibular dysfunction was actually more common than normal vestibular function among the people studied.
It’s not just CANVAS
Many vestibular specialists already know that vestibular dysfunction is common in RFC1-CANVAS (Cerebellar Ataxia, Neuropathy, and Vestibular Areflexia Syndrome), a rare inherited neurological disorder.
As expected, the researchers found that 82% of people with RFC1-CANVAS had bilateral vestibulopathy.
However, one of the study’s most important discoveries was that CANVAS accounted for only about one-quarter of all bilateral vestibulopathy cases.
The remaining cases occurred across many other forms of cerebellar ataxia—including several genetic conditions where vestibular loss had not previously been recognized. Bilateral vestibulopathy was identified in 10 genetically confirmed ataxias beyond CANVAS.
In other words, vestibular dysfunction appears to be much more widespread across cerebellar ataxias than previously appreciated.
Why is this important?
This finding could have meaningful implications for patient care.
Balance problems in someone with cerebellar ataxia are often assumed to result entirely from the cerebellar disease itself. But if vestibular dysfunction is also present—and goes undiagnosed—that person may miss opportunities for treatment.
Unlike many aspects of neurodegenerative disease, vestibular dysfunction can often be addressed through vestibular rehabilitation therapy (VRT).
While VRT cannot reverse cerebellar degeneration, it can help many people improve gaze stability, reduce dizziness, improve balance, and lower fall risk by teaching the brain to make better use of the sensory information that remains.
The researchers therefore recommend systematically assessing vestibular function in all adults with cerebellar ataxia, rather than only those with CANVAS or a few other well-known diagnoses.
An interesting finding: “High” vestibular responses
The study also found that about one in six patients had unusually high VOR gains, meaning their eye movements were stronger than expected.
Scientists do not yet fully understand what causes this finding. Although technical factors can sometimes create falsely elevated measurements, the researchers carefully reviewed every abnormal test to reduce this possibility. They note that increased VOR gain has been reported in cerebellar disorders before, but its clinical significance remains unclear and deserves further study.
What are the limitations?
As with any study, there are limitations.
This research was conducted at a single specialized ataxia center, so the mix of diagnoses may differ from what is seen elsewhere. The researchers also did not measure patients’ vestibular symptoms in detail or evaluate whether vestibular rehabilitation improved outcomes.
Future studies involving multiple centers—and following patients over time—will help determine how much vestibular dysfunction contributes to disability and which rehabilitation approaches are most effective.
What this means for patients
This study reinforces an important message:
Not all balance impairments in cerebellar ataxia arise directly from cerebellar dysfunction; some may instead reflect impaired cerebellar regulation of vestibular function or accompanied vestibular dysfunction.
For many people, vestibular dysfunction may also be contributing to dizziness, unsteadiness, blurred vision with head movement, and falls. Because vestibular problems can often be identified with relatively simple bedside testing or a video head impulse test, asking about vestibular evaluation may help uncover additional contributors to the patient’s symptoms.
For clinicians, these findings support looking beyond the neurological diagnosis alone. Identifying vestibular involvement may lead to more personalized treatment plans that include vestibular rehabilitation alongside other therapies.
While additional research is still needed, this study highlights an encouraging possibility: recognizing vestibular dysfunction could open the door to interventions that improve quality of life for many people living with cerebellar ataxia.
Key Takeaways
- More than half (56%) of adults with cerebellar ataxia had abnormal vestibular function.
- Vestibular dysfunction was found across many different forms of ataxia, not just RFC1-CANVAS.
- Bilateral vestibulopathy was identified in 10 genetically confirmed ataxias, expanding what is known about these conditions.
- Routine vestibular testing—including the bedside head impulse test or video head impulse test—may help identify treatable contributors to balance problems.
- Future research will determine whether recognizing and treating vestibular dysfunction improves long-term outcomes for people with cerebellar ataxia.
