VNS Voice Changes in Epilepsy: What a Systematic Review Found

What was studied

Researchers systematically reviewed 13 studies published from 1993 to 2024 about voice outcomes in people with epilepsy who had implanted vagus nerve stimulation (VNS). The studies included case reports, case series, observational studies, and two controlled comparative studies. The abstract does not report the total number of participants, their ages, or other participant characteristics.

The researchers examined acoustic, perceptual, aerodynamic, phonatory, laryngeal, and patient-reported voice outcomes. Outcomes reported in controlled studies were combined in random-effects meta-analyses, including comparisons between participants with implanted VNS and healthy controls.

What they found

Across the studies, active stimulation was consistently associated with increased jitter and shimmer, shorter maximum phonation time, deterioration in perceived voice quality, and greater self-reported voice-related handicap.

In the combined controlled results, participants with implanted VNS had a maximum phonation time averaging 8.66 seconds shorter than that of healthy controls. They also had significantly higher scores in the functional and physical domains of the Voice Handicap Index. Overall, implanted VNS appears to be associated with clinically relevant alterations in voice function.

Limits of the evidence

The certainty of the evidence ranged from low to very low. Most included studies were case reports, case series, or observational studies, and only two were controlled comparative studies. These findings show associations but do not firmly establish that VNS caused every reported voice change. The abstract does not provide the total sample size, participant ages, VNS settings, length of follow-up, or the extent to which results varied among studies.

For families and caregivers

Voice changes may be an important adverse effect to watch for in people receiving implanted VNS. Possible changes include a less steady voice, difficulty sustaining a sound, poorer perceived voice quality, or voice problems that affect daily functioning. The review suggests that routine voice monitoring should be considered as part of long-term VNS care, but it does not show that every person with VNS will experience these problems or how severe they may be.

What to watch next

Further controlled research could strengthen the evidence and clarify how voice outcomes relate to factors such as VNS settings and length of follow-up.

Terms in this summary

Vagus nerve stimulation (VNS)

An established implanted treatment for drug-resistant epilepsy.

Drug-resistant epilepsy

Epilepsy that has not been adequately controlled with appropriate seizure medicines.

Maximum phonation time (MPT)

How long a person can sustain a voice sound on one breath.

Jitter

Small cycle-to-cycle variations in voice frequency or pitch.

Shimmer

Small cycle-to-cycle variations in voice amplitude or loudness.

Voice Handicap Index

A questionnaire that measures a person's perceived voice-related handicap.

Meta-analysis

A statistical method used to combine results from multiple studies.

Evidence certainty

A rating of confidence in the available body of evidence.