Safety and feasibility of paired vagus nerve stimulation with rehabilitation for improving upper extremity function in people with cervical spinal cord injury: a pilot randomized controlled trial.
Radha Korupolu, Nuray Yozbatiran, Alyssa Miller and 2 others
In six people with chronic cervical spinal cord injury, implanted vagus nerve stimulation paired with arm therapy was safe and feasible.
All three who got active stimulation improved on a hand-function score; none in the sham group did. It was not powered to test efficacy.
Key findings
1No serious adverse events, unresolved device complications, or surgery-related complications occurred through 90 days of follow-up. The only therapy-related events were brief cough during stimulation in four participants across six of 97 sessions, and one episode of bladder spasms in the sham group attributed to a pre-existing urologic issue.
2Four of six participants completed all 18 in-clinic therapy sessions, and overall in-clinic adherence exceeded the predefined 80% threshold. Home exercise adherence over 90 days ranged from 25% to 95% of expected sessions, averaging 59%.
3All three participants in the active VNS group improved on the GRASSP hand-function score after in-clinic therapy, while none of the three in the sham group did. At 90-day follow-up, two of three in the active group met a 6-point improvement threshold; none in the control group did. The authors state these outcomes are exploratory and should not be read as evidence of efficacy.
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What it does not show
Six participants total, three per group. The authors state that formal statistical comparisons, confidence intervals, and effect sizes would be unstable and potentially misleading at this sample size, and that all clinical outcomes are exploratory and hypothesis-generating. Wide clinical heterogeneity: AIS grades B through D, neurological levels C3 through C5, and time since injury ranging from 16 to 61 months. The authors note this limits interpretation of between-group differences. Enrollment was closed at six participants due to budgetary constraints, even though the investigational device exemption allowed up to eight implants. Home exercise adherence varied from 25% to 95% of expected sessions and was not directly monitored during the 90-day home phase. Transportation and access barriers affected recruitment and, in one case, limited in-clinic attendance to 8 of 18 sessions. Spasticity management with botulinum toxin or phenol injections was necessary in some participants, which the authors note may have influenced outcomes. All three sham participants crossed over to active VNS after the 90-day follow-up, so the control group eventually received the treatment. Crossover data were collected for exploratory and ethical purposes only and were not included in primary analyses.
Declared interests
Funded by Mission Connect, a program of the TIRR Foundation. The vagus nerve stimulation devices (Vivistim system) used in the study were donated by MicroTransponder, the manufacturer of the device.
The easy way to misread this
Do not read the GRASSP improvements as evidence that vagus nerve stimulation improves arm function in spinal cord injury. Three participants per group, no formal statistical testing, and the authors' own repeated statement that clinical outcomes are exploratory and hypothesis-generating make this a feasibility study, not an efficacy trial. In addition, all three sham participants crossed over to active stimulation after the 90-day assessment, so the control group eventually received the treatment, and the satisfaction data reflect a population in which everyone ultimately got the active intervention.
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