For the patients with severe vertigo who come to Charles Della Santina’s lab, life is full of constraints. The constant dizziness interferes with their social and working lives mainly because of the limits it places on their mobility—they often can’t walk without a cane and can’t drive cars.
“These people don’t have much hope,” says Della Santina, director of the Vestibular NeuroEngineering Laboratory at the Johns Hopkins School of Medicine. “They come to us after being told by many doctors, you’ll have to learn to live with it, because there’s nothing we can do to help you.”
Della Santina hopes to change that. His lab is currently conducting the first human trials of an inner ear implant that restores patients’ balance by constantly stimulating the vestibular nerves leading to their brains. The team is testing the implants’ safety and efficacy with five patients initially, and hopes to eventually commercialize the device through a spinoff company, Labyrinth Devices.
Only a few vestibular implants have been tried before, and one of those trials had unfortunate results. A study at the University of Washington in Seattle aimed at treating vertigo caused by Ménière’s disease ended early when the first four patients lost their hearing in the ear in which the device was implanted.
But the Johns Hopkins trial has already showed good preliminary results, with no adverse effects. The initial three patients to receive the implant have all experienced improvement, says Peter Boutros, a PhD student in Della Santina’s lab. “When our first subject came to the clinic, he used a walking stick to get around, and if it was dark he had to hold onto his wife or a railing,” Boutros says. At the end of the eight-week study, “he sent us a video of him running on a treadmill.”
The implant is designed to help people with damage to the delicate anatomy that makes up the vestibular system. The inner ear has three tiny structures called semicircular canals that track the head’s rotation along three axes (imagine nodding, shaking your head, and tipping your left or right eyebrow up). Fluid in these canals pushes on sensory hair cells that change the mechanical signal to an electrical one in order to send information up the vestibular nerve.
The initial three subjects in the study had damage to their sensory hair cells due to certain antibiotics that are known to be toxic to the hair cells but are sometimes quite critical to patient care. “Sometimes it’s a life or death situation,” Boutros explains. Patients may be given the antibiotic and, since they’re lying still in a hospital bed, may not notice the onset of dizziness until it’s too late and permanent damage has been done.
To make the device, the team modified an existing cochlear implant used for hearing loss. “There’s roughly a $100-million difference between making an implanted stimulator from scratch and adapting an existing stimulator,” says Santina, because commercial devices have already passed regulatory reviews for safety.
The device includes an external component worn on the head that contains both a gyroscope to track the user’s head rotations in three dimensions and a processor, which sends the rotational data to the internal implant to electrically stimulate the vestibular nerve. The implant uses nine electrodes to convey the information that would normally come from the three semicircular canals.
The patients in this initial trial have the implant in only one ear as a safety precaution, but in a commercial device, users might have implants in both ears for maximum effect. The electrodes continuously stimulate the nerves using an encoding scheme that the researchers customize for each individual patient. Over the course of the eight-week trial, the patients have reported that their vertigo has gradually decreased, which Santina says is a sign that their brains are learning to trust the information coming from the vestibular nerves. “The brain is readjusting to the new normal,” he says.
While the implant could help many people with damage to their inner ears, it won’t help people whose vertigo is caused by problems “downstream” of the vestibular nerve in the brain.
Della Santina says there’s a “special graveyard for people who make overly optimistic estimates about when their device will be approved” by the FDA. But he notes that the vestibular implant should qualify for a humanitarian device exemption, a fast-track FDA approval process that encourages the development of technology for rare diseases. Della Santina is eager to get the device to market so it can help the people who walk into his clinic with little hope: “Our patients who are 60 years old are really eager to get something now, so they can play catch with their grandkids,” he says.