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.