DISCUSSION
The primary goals of numerous treatment options currently used for MD
treatment are first to prevent or at least reduce the frequency and
severity of vertigo attacks, and, secondarily, to prevent disease
progression, treat the effects of end organ damage like hearing loss,
tinnitus, and chronic imbalance, and provide symptomatic relief. A main
consideration regard to the choice of treatment strategy is the
patient’s hearing status, and whether it is usable or not. Nonablative
procedures have been advocated for patients with usable or serviceable
hearing. Surgical procedures for the treatment of this disease can be
classified into three categories. The first category, an ablative
procedure, includes selective vestibular neurotomy or labyrinthectomy.
Although vestibular neurectomy has a very high efficiency of vertigo
control, the risk of operation is high12, and it is
only implemented in patients with total deafness2 and
with an intense desire to receive surgical treatment. The second
category, a traditional functional preserved strategy, involves all
types of endolymphatic sac surgeries (decompression and drainage).
Endolympahtic sac surgery, as a conservative operation, was often used
in intractable MD patients. The theory behind the surgery is to relieve
the pressure of the endolymphatic fluid, thereby decreasing episodic
vertigo attacks induced by endolymphatic hydrops13,14.
So far, endolymphatic sac surgery has been universally acknowledged and
used, and has generally considered to be a safe surgical option because
hearing is maintained postoperatively13,15. However,
many patients relapsed with episodic vertigo postoperatively, and the
control rate of vertigo was only 60~80%; the benefit of
this strategy is still under debate as it yields inconsistent results
compared to placebo surgery16,17.
The third category is semicircular canal occlusion/plugging, a novel
procedure proposed for the management of intractable peripheral vertigo
by many specialists, which aims to
block the movement of endolymph in
the canals and therefore
to
eliminate vertigo attacks induced by position
changing3. Since semicircular canal occlusion was
first applied to treat intractable benign paroxysmal positional vertigo
in 1990, many investigators have begun to apply this method for the
treatment of intractable peripheral vertigo, with results showing that
plugging surgery represents a safe option 18. However,
the investigation of semicircular canal plugging/occlusion applied to
patients suffering from MD has scarcely been discussed to date. Yin et
al19 applied TSCO to three patients with MD who
underwent unsuccessful ESD or a mastoid shunt, demonstrating that two
cases reached complete vertigo control with the other reached
substantial vertigo control. In this study, TSCO combined with ESD was
applied to patients with intractable MD as the primary surgical strategy
for the purpose of controlling vertigo. The overall vertigo control rate
was 100%, with a complete control rate of 97.8% and a substantial
control rate of 2.2%. The vertigo control rate was higher than the rate
reported by Zhang et al20,21 and Charpiot et
al22. All patients in this study were satisfied with
the vertigo control postoperatively during the follow-up period. Our
data directly suggested that combining TSCO and ESD is an efficient
strategy for vertigo control in patients with intractable MD.
As a nonablative procedure, TSCO combined with ESD provided a satisfying
vertigo control rate in this study. However, the total hearing
preservation rate was 82.61%, 73.91%, and 54.35% at 6-months,
12-months, and 18-months postoperative, respectively. This was
inconsistent with the data from Zhang20, who reported
a rate of 70.9% for hearing preservation in a 2-year follow-up.
However, 76.19% of patients were in stage III (16/21) and 41.67% of
patients in stage IV (5/12) with hearing loss, no patients in stages I
or II pre-operatively (13 patients) complained of hearing loss
postoperative. The results of this study suggested that patients in
advanced stages (stages III and IV) suffered more from progressive
hearing deterioration postoperatively as time elapsed, which suggested
that vertigo control cannot simultaneously halt the progression of
cochlear function deterioration. Although the group of patients suffered
from hearing deterioration including 15 patients who presented with no
serviceable hearing function pre-operatively (Table 4). However, this
group of patients lost the opportunity to use the hearing aids to
improve their social communication in daily life. Residual hearing
preservation remains a significant challenge to address prior to the
selection of an optimal strategy for intractable MD patients.
Why does hearing deteriorate over time? Animal studies demonstrated that
factors such as lymph leak, bleeding into the inner ears, serous
labyrinthitis, and infections were all considered to potentially induce
hearing loss during surgery23,24. Hearing loss caused
by those factors is reversible25. However, transaction
of the membrane labyrinth intraoperatively usually causes irreversible
hearing loss25. Otherwise, in our study, all patients
suffered from hearing loss postoperatively were in stages III and IV. In
this case, it remains difficult to determine exactly what the factors
affecting the auditory function directly are postoperatively. Our data
do not support the notion that the surgery procedure itself, or the
labyrinthitis postoperatively, directly deteriorated the hearing.
Blocking the movement of endolymph in the canals can eliminate vertigo
attacks induced by position changing but cannot halt the development of
MD on cochlear function deterioration, especially at advanced stages.
Whether surgery, disease stages, or other potential risks (such as aging
and lifestyle) were factors directly inducing hearing loss over time
postoperatively still needs to be further investigated. A long-term
follow-up is necessary to investigate the auditory function
postoperatively.
The aural fullness remission was
consistent with the vertigo control in this study. The tinnitus control
rate is 65.8%. Patients still bothered with persistent or bothersome
tinnitus had severe hearing loss. However, this cannot rule out the
possibility that tinnitus is related to auditory function damage in MD.
In this study, 30 patients regained their balance within 2 months, with
an average recovery time of 12.6 days. There were 4 patients who still
felt unstable or like they were floating at the latest follow-up
interview because none of these 4 patients persisted with vestibular
rehabilitation postoperatively. Vestibular rehabilitation is important
and effective for vestibular function compensation in patients
postoperative. The vestibular dysfunction induced by TSCO and ESD is
reversible, and vestibular rehabilitation should be recommended to all
patients postoperative.
In conclusion, combining TSCO and ESD is an efficient strategy for
vertigo control in patients with intractable MD. However, the hearing
functions were deteriorating gradually postoperatively in patients at
advanced stages. The hearing preservation and tinnitus relief still
warrant further illumination.