Vestibular implantation in older adults

Project Summary Bilateral loss of vestibular sensation is disabling, with affected individuals suffering chronic disequilibrium, increased risk of falls, and inability to maintain stable vision during head movements typical of daily life. Most individuals with mild or moderate loss compensate through rehabilitative strategies enlisting other senses; however, those with severe loss who fail to compensate have no good therapeutic options. For older individuals who are already contending with decreases in vision, proprioception and other systems that normally contribute to maintaining balance, lack of compensatory reserve can make loss of vestibular sensation even more impactful. Fortunately, when the vestibular nerves are anatomically intact, as is true in most such cases, electrical stimuli encoding head rotation can artificially drive nerve activity to partially restore vestibular sensation, much as a cochlear implant partially restores auditory sensation. In the first-in-human early feasibility study designed to test the safety and efficacy of long-term prosthetic vestibular nerve stimulation as a sensory restoration treatment, we performed unilateral vestibular implantation in 8 adults aged 51-66 years old who had been disabled for 2-23 years by bilateral vestibular hypofunction. We found that vestibular implantation and 24 hr/day motion-modulated prosthetic stimulation targeting the three implanted semicircular canals drives directionally-aligned vestibulo-ocular reflexes, improves objective measures of posture and gait, and improves patient-reported dizziness handicap and vestibular-related disability. However, we do not yet know whether this sensory-restoration treatment will work well in older adults, who are thought to have greater difficultly adapting to asymmetry in input from the two vestibular labyrinths. Drawing on an established design, experienced study team and protocol that have already yielded highly impactful results in the existing study of younger subjects, the proposed research will extend this approach to older adults disabled by bilateral vestibular hypofunction. Results are very likely to yield sustained impact, by clarifying the relative risks and benefits of this intervention in older adults and by providing data that can inform decisions by regulators, policy-makers and third-party payers regarding whether older adults disabled by bilateral vestibular loss should have access to vestibular implantation.