Tinnitus suppression with electrical stimulation in subjects with Single Sided Deafness

(this text is taken from the protocol, for references see protocol)

Tinnitus (Aurium) is a symptom characterized by the perception of sound or
noise in the absence of any objective external physical source. This disorder
affects millions of people worldwide; its precise pathophysiologic mechanism is
unknown. It has yet remained refractory to current medical treatment. It is
supposed that tinnitus might be suppressed by restoring peripheral auditory
neural activity. In clinical practice, conventional hearing aids are often used
for this purpose with only limited success.

Scarce studies in a limited number of patients show that electrical stimulation
of the (vestibulo)cochlear nerve proves beneficial in some cases[1-12]. The
effect of peripheral electrical stimulation seems to depend on finding and
applying the optimal stimulation pattern, as well as creating an optimal
electroneural interface (i.e. the coupling of the electrode to the auditory
nerve)[10,13].

We propose to stimulate the cochlear nerve by using cochlear implant (CI). A CI
is a multi-channel device implanted in the cochlea which makes it possible to
apply frequency- and amplitude specific stimuli to the cochlear nerve. It
provides a relatively good electroneural interface and a lower surgical risk
compared to direct stimulation of the auditory nerve.

To achieve speech understanding, the CI is programmable in various frequency
bands. This feature enables us to program various electrical stimulation
patterns to achieve tinnitus suppression. Thus, using CI for tinnitus
suppression enables a more customised, patient-specific treatment, compared to
direct neural stimulation. Moreover, applying a CI might also create
possibilities to develop a tinnitus implant, enabling treatment for a
debilitating condition for which currently no treatment is available.

In current CI-recipients who suffer from pre-implant tinnitus and who are
profoundly deaf, generally a suppressive effect on tinnitus is reported in 65%
to 93% of cases[2-12]. This suppressive effect may be caused by the electrical
stimulation itself or by the shift in patient*s attention from the tinnitus to
environmental sounds[14].

(this text is taken from the protocol, see protocol for the detailed version)

The main objective of the study is to gain insight in the underlying mechanism
of tinnitus suppression. This objective will be achieved by comparing the
suppressive effect of a *simple electrical stimulation* pattern (i.e. without
environmental sound perception) with the *standard stimulation pattern* of a CI
(i.e. with environmental sound perception), in SSD-patients. A secondary
objective is to investigate whether either of the two can be maintained over
time.

(this text is taken from the protocol, see protocol for the detailed version)

There are indications that the optimum simple electrical stimulation pattern is
subject specific. Therefore, a fine tune procedure will be performed to obtain
the optimal stimulation pattern for each individual patient[15,16].
Subsequently, subjects will be assigned to one of two study groups. In group I,
simple electrical stimulation will be followed by conventional CI usage, while
in group II, conventional CI usage will be followed by simple electrical
stimulation. After this crossover design the treatment modality of choice,
either simple electrical stimulation or conventional CI, can be chosen by the
patient. Outcomes will be analyzed between alternating conditions.

(this text is taken from the protocol, for the detailed version or a schematic
overview (Flow-chart and table 1) see protocol)

Through a standard surgical procedure subjects will receive a CI in the
ipsilateral deaf ear. After implantation and standard CI-fitting, a fine tune
procedure will be performed to obtain the optimal stimulation pattern for each
individual patient. Subsequently, the long term effect of either of both modes
will be assessed in the crossover study. Finally, patients are able to choose
their most comfortable treatment modality.

(this text is taken from the protocol, for the detailed version or risk
analysis see protocol)

Participants will undergo audiometry and clinical imaging (MRI) as part of the
routine diagnostics in single sided deafness. Cochlear implantation is a
routine surgical procedure carried out about 80 times each year in the azM in
children and adults, under general anaesthesia. The risk of major and minor
complications associated with this surgical procedure is low in the azM
compared to the literature[17]. Risks are wound infection, temporary
dysbalance, temporal ipsilateral facial nerve palsy and permanent loss of
residual hearing in the affected ear, if any residual hearing is present.

All electrical stimulation patterns in the study will be applied using the
standard CI-processor, remaining well within its conventional, clinical safety
limits. Cochlear implantation involves highly patient-specific fitting,
assuring that all stimulating patterns are optimized for each patient. The
non-invasive audiological- and tinnitus-specific tests, plus various
questionnaires at predetermined times take time and effort: ca 2 hours per
visit, with a total of 20 visits.

Literature shows that cochlear implantation in SSD-patients provides a
significant improvement in speech perception, specifically in spatial
conditions, as well as in directional hearing and localization[18-21]. Also,
the long term suppressive effect of the standard CI-processor (i.e. with
environmental sounds perception) on tinnitus has been reported in certain cases
and will possibly provide individual benefit for the included
participants[22,23].