gms | German Medical Science

Bilateral vestibulopathy is a medical condition in which both vestibular systems are not functioning properly. This can lead to a variety of symptoms, including oscillopsia, imbalance, and impact several cognitive functions [1]. Consequently, this reduces quality of life and has a big socieoeconomic burden. Vestibular rehabilitation may alleviate the impact, but this is limited. Unfortunately, no cure is available yet.

This encouraged several research groups around the world to investigate the possibility of restoring vestibular function with an artificial balance organ: a vestibular implant. The concept is analougous to a cochlear implant. Instead of sound, motion is captured through motion sensors, such as gyroscopes and accelerometers. This information is transferred through an electrical current to electrodes that are surgically placed close the vestibular sensory epithelium. Most research groups are investigating stimulation of the ampullary nerves of the semcircular canals, but also stimulation of the otolith organs is being investigated.

The Geneva-Maastricht group was able to electrically stimulate the semicircular canals and demonstrated the elicitation of a vestibulo-ocular reflex in the plane of the stimulated semicircular canal, leading to improvement of dynamic visual acuity[2]. This could be elicited for both slow and fast head movements and this electrical vestibulo-ocular reflex mimicked the natural vestibulo-ocular reflex. It was also found that the brain was able to adapt to baseline stimulation, while still responding to motion-modulated stimulation. Additionally, vestibulocollic reflexes and other postural responses could be elicited. Several of these findings were later also found by other research groups and therefore indicate reproducibility with different vestibular implant prototypes. This demonstrates the feasibility of a clinically applicable vestibular implant.

However, several challenges still remain. One challenge is to minimize the impact on residual inner ear function, in particular hearing. The Geneva-Maastricht group only implanted patients with (at least single-sided) deafness, with a combined vestibulo-cochlear implant, in order to avoid potentially inducing severe hearing loss. Other research groups implanted patients with residual hearing with a vestibular implant, leading to various results, ranging from a very limited hearing loss to a very severe hearing loss or deafness. Another challenge is correct electrode placement. The ampullary nerves can be reached either directly, with a challenging extralabyrinthine approach, although this is not possible in every patient, or through the semicircular canals (intralabyrinthine approach). This latter approach is hampered by limited visualization of the target. Therefore current research also focuses on improving electrode placement, such as with radiological guidance [3].