Implant Produces ‘Remarkable Improvement’ in Vestibular Disorder
Implant Produces ‘Remarkable Improvement’ in Vestibular Disorder
An implanted device is showing promise in patients with bilateral vestibular hypofunction (BVH), a debilitating condition that significantly impairs balance.
Early research suggests the modified cochlear implant placed in the inner ear of eight patients with BVH improved balance, movement, and quality of life in as little as 6 months.
“We found remarkable improvement in performance on standardized clinical tests of balance and walking following implantation,” study investigator Margaret Chow, a biomedical engineering doctoral candidate, Johns Hopkins University, Baltimore, Maryland, told Medscape Medical News.
“All participants reported improved quality of life and being able to engage in activities they thought they would never be able to do again, and all participants agreed to continue using the device beyond their planned study period,” Chow said.
The study was published online February 11 in the New England Journal of Medicine.
“Approximately 1.8 million adults worldwide have severe BVH, resulting in chronic disequilibrium, oscillopsia, postural in stability, and unsteady gait, owing to failure of vestibular reflexes that stabilize the eyes,” the authors note.
Senior investigator Charley Della Santina MD, PhD, professor of otolaryngology, head and neck surgery and biomedical engineering at Johns Hopkins University, told Medscape Medical News that while we are taught that we have five senses, “we actually have a ‘sixth sense,’ which is the ability to know how to move through the world — something we’re not even aware of unless we lose it.”
Individuals with BVH have lost the small hair cells in the inner ear that encode the motion of head rotation and convey them to the vestibular nerve. These hair cells are similar to the cochlear hair cells that encode sound.
“Without that vestibular ability, people with BVH have trouble keeping their eyes, head, and body steady,” Chow said. “They look ‘normal’ and have no obvious deficits, but they can’t walk properly or see clearly when their heads move.”
The “wobbling gait gives the appearance of intoxication, leading to social stigma. The amount of concentration required to walk is taxing; and the cognitive distraction increases fall risk.”
BVH can be idiopathic or caused by a number of conditions, including Meniere’s disease. However, in roughly one third of patients, the dysfunction is a side effect of antibiotics, particularly aminoglycosides, which are toxic to the inner ear.
Current treatment approaches to BVH involve vestibular rehabilitation, avoiding ototoxic and sedating medications, and avoiding activities that increase risk of injury. Noninvasive devices using sound, skin vibration, or galvanic stimulation can help with postural instability but not with gait.
Patients with BVH at other centers have undergone similar implantation, but the devices were tested only in the laboratory setting, while in the current study, the device was worn 24 hours a day over a 1-year period.
“Our device bypasses damaged hair cells in the dysfunctional semicircular canals, electrically stimulating vestibular nerve branches,” Della Santino explained. The electrical current pulses “vary in rate and amplitude, depending on the rotation speed and axis of the head.”
Chow noted the device was implanted unilaterally rather than bilaterally, although BVH affects both ears, because of concerns that it might adversely affect the patient’s hearing.
The median (range) age of the eight study participants was 59 (50–60) years. Of these, seven had adult-onset BVH caused by use of an aminoglycoside, while one had idiopathic hypofunction.
Testing took place at baseline, and then at 6 months and 1 year post-implantation. Two patients were unable to complete 1-year testing, due to pandemic-related travel limitations.
Participants showed higher scores between baseline and 6 months on two posture/balance tests, with a median improvement of 5.5 (95% CI, 0–10.0) and 5.1 (95% CI, 1.5–27.6) points on the Bruininks-Oseretsky Test of Motor Proficiency and the modified Romberg test, respectively.
They also showed improvements in gait, with a median increase of 10.5 (95% CI, 1.5–12.0) points on the Dynamic Gait Index and 2.3 (95% CI, –1.7. to 5.0) seconds on the Timed Up and Go test.
The score on the Dizziness Handicap Inventory improved by a median within-participant difference of 50 points. Improvements were also seen for activities of daily living and quality of life.
Median within-participant changes from baseline to 1 year were “generally consistent” with results at 6 months.”
Placebo-mode testing corroborated the treatment-mode stimulation’s role in these improvements.
Although all patients experienced some hearing loss in the implanted ear, five continued to be able to use a telephone without a hearing aid and only three experienced greater hearing loss.
“The benefits weren’t only seen on clinical tests — some patients have returned to enjoyable activities they were previously unable to do, such as riding a bike, gardening, or walking on uneven terrain at the beach, and two were able to dance at their daughter’s wedding,” Chow said.
Commenting on the study for Medscape Medical News, Daniel Lee, MD, associate professor, Department of Otolaryngology, Harvard Medical School, Boston, Massachusetts, said that although the findings are “early,” they “support the safety and tolerability of a multichannel vestibular implant and pave the way for future long-term studies with greater numbers of patients across multiple centers.”
The study “also highlights the risk of loss of residual hearing in patients who receive the vestibular implant — not an unexpected finding, given the inherent fragility of the inner ear in these cases,” said Lee, who is also director of pediatric otology and neurotology at Massachusetts Eye and Ear and was not involved with the study.
Also commenting on the study for Medscape Medical News, Richard Lewis, MD, associate professor of otolaryngology–head and neck surgery and neurology, Harvard Medical School, noted that this approach “only works when the damage is in the inner ear, but the nerve connecting the ear to the brain — the eighth cranial nerve — is still functioning fairly normally.”
By contrast, “the surgery wouldn’t work if the pathology is in the nerve itself,” said Lewis, who was not involved with the study.
Della Santina noted that patients in their study were all in their 50s and 60s. Future research will include older patients and, ultimately, children.
Chow recommended viewing a videoed interview of patients to gain further insight into the impact that implantation had on them.
The study was supported by the National Institute on Deafness and Other Communication Disorders of the National Institutes of Health, by Labyrinth Devices, and by MED-EL. Della Santina reported being the fiduciary officer at Labyrinth Devices and receiving institutional grants from Labyrinth Devices and Med-El. His other disclosures are listed on the original paper. Lee chairs the clinical advisory board of Frequency Therapeutics. Chow and Lewis have disclosed no relevant financial relationships.
N Engl J Med. 2021;384:521-532. Abstract
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