Middle ear implantable devices in tinnitus treatment
- Tinnitus is often associated with high-frequency hearing loss.
- Rehabilitation with hearing aids has shown effectiveness in reducing tinnitus. However, in some individuals with severe high-frequency hearing loss, classical hearing aids are not always able to amplify the high frequencies sufficiently and provide enough power.
- Active middle ear implants are an alternative to conventional hearing aids that allow more power delivered to the cochlea, especially at high frequencies, and can also be used when middle ear ossicles are damaged.
- A study supported by the Tinnitus Research Initiative (TRI) and MED-EL of the effect of a middle ear implant showed that individuals with severe tinnitus and high-frequency hearing loss achieved relief of their tinnitus after implantation.
- Some patients had complete relief of their tinnitus after activation of the middle ear implant. Similar effects cannot be achieved by conventional hearing aids.
- Individuals who have significant residual inhibition of their tinnitus and high-frequency hearing loss seem to be the best candidates for implantations.
Individuals with tinnitus, who also suffer from hearing loss, often benefit from amplification. The use of hearing aids in tinnitus patients may make the patient less aware of the tinnitus as well as improve communication by reducing masking by the tinnitus. Hearing aids may also reduce the tinnitus, because they provide input to the nervous system that may reverse some of the plastic changes from deprivation of sound that has caused tinnitus and may counteract the deprivation of sound that causes some forms of tinnitus.
It has been reported that up to 67% of individuals who received unilateral hearing aids and 69% of individuals who received bilateral hearing aids report improvement in their tinnitus .
The quality of sound contributes many aspects. The effect of the pinna and the resonance in the external auditory canal contribute to optimize gain at higher frequencies .
Hearing aids often increase the perceived quality (color, crispness, clarity, pureness) of sounds, which could be important in reducing tinnitus annoyance, but unfortunately is not measured in routine clinical practice and is difficult to define.
Today’s digital hearing instruments are very advanced, offering maximum performance and reducing many of the difficulties encountered in earlier designs. In past years, improvements in hearing devices have substantially helped control feedback, widening the frequency range, and, to some degree, have improved sound quality. However, some individuals still experience the stigma and practical problems of using these devices.
Traditional hearing aids lack amplification of high frequencies (above 6,000 Hz) and fail to provide sufficient power. This is a problem in connection with suppression of tinnitus, which requires that high-frequency sounds are delivered to the ear at sufficient intensity.
Good reproduction of high-frequency sounds is also necessary for directional hearing and hearing when background noise is present.
Using a conventional “loudspeaker” at the end of the amplification chain seems to be the limiting factor for a sophisticated development of these devices.
Relocating the loudspeaker to the outer ear canal increased the performance of amplification in the high frequency range.
Recognizing these problems and the fact that sound quality will always be an issue for those who use traditional hearing instruments and individuals with tinnitus, promoted the development of active middle ear implants. This has solved many of the problems of traditional hearing aids. It was therefore of great advantage in the treatment of some forms of tinnitus, occurring together with hearing loss, when devices that provide sound delivered directly to the middle ear bones or directly into the cochlea were developed. The amplification and the power that can be delivered to the cochlea using such devices exceed those of conventional hearing aids. Particularly, amplification is achieved in a larger frequency range than what is possible using traditional hearing aids.
With customized active middle ear implants, there is no need for a “loudspeaker” (receiver), thus reducing the distortion and reduction in the quality of sounds that occurs in traditional hearing aids. Furthermore, the ear canal is never occluded when implantable hearing aids are used.
History of Implantable Hearing Aids
Middle ear implants started in 1935 when Wilska  experimented with iron particles placed on the tympanic membrane. Wilska generated a magnetic field from an electromagnetic coil inside an earphone, which caused the iron filings to vibrate in synchrony with the magnetic field. This vibration in turn caused the eardrum to vibrate and allowed sound to be transduced to the cochlea in normal fashion. Later, Rutschmann (1959)  successfully stimulated the ossicles by gluing 10-mg magnets onto the umbo. An electromagnetic coil created a magnetic field that caused the ossicles to vibrate. Devices actually placed into the middle ear did not appear until 1970s .
Today, three general types of transducers are used in middle ear implants, each with advantages and disadvantages related to power, performance, frequency range, and reliability. The types of transducers used in middle ear implants consist of piezoelectric, electromagnetic, and electromechanical transducers.
Yanagihara and his colleagues  described an implantable piezoelectric device attached to the head of the stapes and performed the earliest human trials using these devices [7–12]. Their device was intended for patients with conductive and sensorineural loss.
A totally implantable piezoelectric device, known as the Esteem Hearing implant , was developed by St. Croix Medical, Inc. (now Envoy Medical Corporation) (Picture 1).
Picture 1: Envoy piezoelectric device - “Esteem”
Electromagnetic transduction devices consist of a magnet and an energizing coil. The magnet is attached to the ossicular chain, tympanic membrane, or the inner ear (round window or oval window). Specific experiences with regard to the influence on tinnitus have not been published.
Another implantable middle ear device known as Carina™ is shown in Picture 2.
Picture 2: Otologics MET fully implantable middle ear device - “Carina”
Soundbridge is the middle ear implant with the longest clinical experiences, 3,000 patients so far (2009). It was first marked by Symphonix Devices in San Jose, California, as the Vibrant Soundbridge. It has received both European CE-mark in March 1998 and FDA approval in the U.S. in August 2000 [14–16]. However, the company went out of business in 2002 only to return in March 2003 as the Med-EL Vibrant Soundbridge.
The semi-implantable device consists of an outward audio processor which is placed over the implanted coil and magnet. The coil is linked by a golden wire to the floating mass transducer (FMT) (Picture 3). The frequency range is 1,000–8,000 Hz, but technically amplification up to 16,000 Hz is possible.
Picture 3: The “vibrant soundbridge” system
In the last few years, the Vibrant Soundbridge has assumed particular importance through the fact that the FMT can also be implanted in the round window  (Picture 4). The indication here refers to a destroyed middle ear, such as after removal of the petrosal bone, malformations, cholesteatoma, sclerosis of the footplate, etc. The FMT provides a better way to induce sound energy into the cochlea than using the ossicular chain.
Picture 4: Implantation of an FMT into the round window
A special form of implanting the FMT was achieved by Hüttenbrink with “TORP-Y-Vibroplasty” .
Tinnitus-Related Clinical Observations and Studies
In the ENT Clinic in Traunstein, 52 patients have been equipped with the implant since 1998 (four of them bilaterally). All patients were provided with conventional hearing aids before and, for different reasons, were not content with these devices. All patients continue to use their middle ear implant as of August 2009 without any technical problems. It was surprising that most patients, who simultaneously suffered from tinnitus, reported that the middle ear implant largely reduced their tinnitus which could not have been achieved by traditional hearing aids.
In 2000, a patient implanted on both sides with middle ear implants reported that this tinnitus disappeared completely after activating the implant. Six years later, inspired by the results obtained by the middle ear implant in this person, the Tinnitus Research Initiative (http://www.tinnitusresearch.org) offered a grant to study the effect of the middle ear implants on tinnitus. The participants had sensorineural hearing loss at high frequencies and tinnitus and had been given middle ear implants. All patients reveived the Vibrant soundbridge. They were studied for 1 year using a visual analogue scale (VAS), Goebel–Hiller score , and the Tinnitus Handicap Inventory (the German TBF-12 [20, 21]).
The first patient was implanted in January 2007 on the left side. His audiogram showed severe hearing loss on the left side and minor hearing loss on the right side (Picture 5). The combination, with a good dynamic range assessed by the level of discomfort, gave a good indication for implantation.
Picture 5: Audiogram of patient before first implant operation
After the operation, the audio processor was activated, and the reaction of his tinnitus was surprising: the tinnitus shifted from his left side to his right side.
Picture 6 shows the result: because of the remaining tinnitus, there was no improvement regarding annoyance after 2 months, and the person did not develop any habituation. Facing the fact that this individual now had tinnitus on the right side, we also implanted the right side with the Soundbridge 12 weeks after the original implantation. With the activation of both audio processors, the annoyance due to tinnitus diminished, and the quality of life improved.
Picture 6: Audiogram of same patient after first operation
Picture 7 shows the functional gain (green line) after the implantation of the Soundbridge in both ears. The patient describes that his tinnitus decreases already by switching on the device, although he is not able to hear the receiver noise. This indicates that in addition to a masking effect, there might be other effects from the implanted device.
Picture 7: Audiogram of same patient after second implant operation
At the 1-year follow-up exam (patient “M.A.”), this patient is no longer annoyed by tinnitus when the audio processor is activated.
The first patient of a new study, sponsored by the company Med-El® with five participants with unilateral tinnitus and reproducible residual inhibition, received a Soundbridge implantation in June 2008. The device was activated and fitted in August 2008. Immediately after the fitting process, the patient’s tinnitus disappeared completely after switching on the device. Although they were once greatly bothered and annoyed by the tinnitus, the activation of the device gave complete relief.
Three other participants in this study reported similar effects.
Implantable hearing aids have shown to be effective in reducing tinnitus in individuals with severe hearing loss and tinnitus, where the hearing loss was caused by middle ear or cochlear pathologies. The reason the middle ear implantable devices provide relief of tinnitus may be masking, but it seems more likely that the benefit is caused because these devices provide effective activation of the auditory nervous system, and thereby counteract the effect of deprivation of sound input that had activated neural plasticity causing the tinnitus. This means that the effect of the implanted hearing aids on tinnitus is similar to that of cochlear implants.
One reason for the success of implantation might be that it facilitates residual inhibition.
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