Individuals with bilateral vestibular hypofunction (BVH) have difficulty maintaining balance and stabilizing their head, body, and vision (Vestibular Disorders Association, 2021). This disease affects approximately 1.8 million adults worldwide who have great difficulty standing and appear to “walk like a drunk” (Vestibular Disorders Association, 2021; Ward et al, 2013). Quality of life is severely decreased in these individuals, and existing treatments are not always effective (Sienko et al, 2017; Krebs et al, 2003). In a 2021 paper published in The New England Journal of Medicine, Chow and colleagues at the Johns Hopkins School of Medicine tested a newly developed vestibular implant that provides fine-tuned artificial sensation of balance by directly stimulating the vestibular nerve. They found the device offered significant improvements in standardized posture and gait tests, as well as higher self-reported quality of life in the eight participants. The implications of these findings are significant as they demonstrate the efficacy of a potential treatment for those with BVH. 

Background

BVH occurs when the portion of our inner ear that gives us a sense of balance (called the semicircular canals) does not function properly. This is often due to sensory hair cell death within these semicircular canals, which can be caused by antibiotics or autoimmune disorders (Ward et al, 2013). Current treatment options for those with BVH include rehabilitation exercises and galvanic stimulation via skin electrodes around the external ear (Brown et al, 2001; Wuehr et al, 2017). However, in individuals with severe BVH, neither of these are effective enough to facilitate coordinated actions like walking (Krebs et al, 2003; Sienko et al, 2017). In the last few decades, cochlear implants have been developed to treat hearing loss by bypassing cochlear hair cells and directly stimulating branches of the auditory nerve (Deep et al, 2019). In recent years, scientists have begun investigating a similar implant device for those with BVH, hoping to bypass damaged semicircular canal hair cells and directly stimulate sections of the vestibular nerve. Prototypes showed success in chinchilla and rhesus monkey models (Della Santina et al, 2010; Dai et al, 2011). Building on the success of animal prototypes, Chow and colleagues set out to test a new vestibular implant device in humans with BVH.

Methods

In the study, eight persons (three men, five women) with BVH underwent baseline testing for balance, gait, and self-reported quality of life. Tests included balancing on one foot, standing feet-together with eyes closed, walking heel-to-toe along a line, completing a timed walking task though an obstacle course, and filling out a quality of life-questionnaire. The individuals were then fitted with a vestibular implant system, consisting of a surgically implanted array of inner ear electrodes in one ear, an external gyroscopic sensor attached to the skull, and a power unit strung around the neck. Inner ear electrodes were implanted in three strategic locations in vestibular nerve, each associated with a 3-dimensional axis of movement. The device was worn and activated 24 hours a day. Balance, gait, and quality of life tests were repeated 6 months and 12 months after implantation. Tests were completed several times with the device turned off and on (unbeknownst to the participant) to eliminate the placebo effect (Chow et al, 2021). 

Results

Participant balance improved significantly after implantation, as indicated by higher test scores. Before implantation, participants could only stand with their eyes closed for an average 3.6 seconds before losing their balance, compared to 14.5 seconds one year after implantation. Participant walking ability also significantly improved, with gait speed increasing 18% one year after implantation. Scores on the “walking obstacle course” improved from 12.5 before implantation to 22.0 after implantation (on a scale of 0-24, with 24 indicating perfect performance). A quality-of-life questionnaire also showed significant improvements in overall quality of life among all participants. 

Discussion

The study clearly found that the implant significantly improved all three metrics of measurement – balance, gait, and quality of life. When the device was turned off during 6- and 12-month testing (unbeknownst to participants), balance and gait scores decreased to pre-implantation levels, indicating the improvements were not due to the placebo effect or neuronal regeneration in the semicircular canals. Albeit subjective, it should be noted that all participants said they had an easier time completing daily living activities after implantation, which extends the findings of this study beyond a laboratory setting (Chow et al, 2021). It should be noted that the implantation surgery slightly damaged 7 of the 8 participants’ hearing, as hearing threshold increased an average of 8 decibels after the procedure (Chow et al, 2021). However, all 8 participants stated that the hearing compromise was “worth it,” and if given the choice they would repeat the procedure (Chow et al, 2021). While this novel device has its shortcomings, this study provides a novel, effective way to enhance the quality of life for individuals with BVH. Beyond BVH, this study advances progress in the treatment of sensory diseases by bypassing sensory cells to artificially stimulate nerves – a development that takes us one step closer to artificial sensation. 
 

Figure: Summary of Methods and Results

[+] References

[+] Other Work By Forrest Fearington