Comparisons of cochleotoxicity among three gentamicin compounds following intratympanic application

Conclusion. Among the three main gentamicin (GM) compounds following intratympanic application, the cochleotoxicity of C2 was the most severe, whereas that of C1a was the weakest. Understanding of the different cochleotoxicity characteristics of each compound may be of use in future custom-made intratympanic therapy for Ménière's disease. Objective. To investigate differences in cochleotoxicity among three major GM compounds following intratympanic application. Materials and methods. Three GM compounds (C1, C2, and C1a) were isolated. Sprague-Dawley rats were treated every 2 days for 2 weeks with intratympanic application of saline, GM complex, C1, C2, and C1a. The cochleotoxicity of each compound was assessed by measuring auditory brainstem response (ABR) and through morphological analyses using scanning electron microscopy. Results. The ABR threshold of the C2 group was found to be more impaired than those of the other groups. The C1a group showed the mildest elevation of the ABR thresholds. Morphological analyses revealed that the proportion of remaining outer hair cells (OHCs) was the lowest in animals treated with C2. Morphologically, the C1 and C1a groups showed the least damage to OHCs.     

Early ultrastructural effects of gentamicin cochleotoxicity

Ultrastructural changes in the cochlear hair cells during the early stages of gentamicin intoxication were investigated after tri-aldehyde primary fixation and OSO4/K4Ru(CN)6 post-fixation. In cochleas treated for 5, 10 and 15 days with gentamicin the individual outer hair cells (OHC1, OHC2 and OHC3) were randomly affected. Degeneration of the inner hair cells was not observed at this stage. Ultrastructurally, the earliest identifiable changes were an increase in lysosomes, proliferation of the endoplasmic reticulum, and formation of Hensen's bodies. This was followed by dilatation of the endoplasmic reticulum and the nuclear envelope, giving rise to extensive cytoplasmic vacuolation. These results demonstrate that gentamicin-induced changes primarily involve the cell's synthetic apparatus. All further intracellular changes occur at a much later stage and are therefore to be considered secondary events.     

Time course of apoptotic cell death in guinea pig cochlea following intratympanic gentamicin application

CONCLUSIONS: The present study showed that the molecular signal that promotes the death of cochlear hair cells (HCs) induced by intratympanic gentamicin application is significant before the manifestation of morphological and functional changes. OBJECTIVES: The effect of agents that protect the HCs from aminoglycoside ototoxicity is influenced by the timing of their administration. However, morphological, functional and molecular changes in the cochlea in the early stage following aminoglycoside application have rarely been studied. Therefore, we examined the chronological changes in the cochlea following intratympanic gentamicin application. MATERIALS AND METHODS: Small pieces of gelatin sponge soaked with gentamicin (40 mg/ml) were placed on the round window membrane of mature guinea pigs, and the tympanic bulla was filled with gentamicin solution. They were euthanized at 6, 12, 18, 24, and 48 h following gentamicin application. Auditory brainstem responses (ABRs) were measured before gentamicin application and immediately before euthanasia, and the extent of missing and TUNEL-positive HCs was evaluated. RESULTS: ABR thresholds significantly increased 18 h or later following gentamicin application, and the loss of HCs was seen at 24 and 48 h. While functional and morphological changes were not evident until 18 h after gentamicin application, substantial amounts of TUNEL-positive HCs appeared at 12 h.     

庆大霉素鼓室内注射后在内耳细胞中的分布

目的 观察鼓室内注射庆大霉素后，不同时间庆大霉素在前庭和耳蜗中的分布。方法 将庆大霉素同德州红连接形成庆大霉素-德州红耦联物后，行豚鼠鼓室内注射，注射后12h，1、2、3、4、7、14、28d处死动物，Phalloidin染色后运用激光共聚焦扫描显微镜观察基底膜、椭圆囊、球囊、外半规管壶腹嵴庆大霉素分布情况，并进行荧光分布半定量分析。结果 庆大霉素自注射后12h起在内耳所有细胞均见分布，在基底膜的外毛细胞、椭圆囊、球囊、外半规管壶腹嵴的感觉细胞聚集明显，主要聚集在毛细胞顶端纤毛下方的细胞质中，支持细胞分布较少。注射后第3天庆大霉素在内耳聚集达到最高峰，并在毛细胞内聚集较长时间。结论 庆大霉素-德州红耦联物是一个研究庆大霉素在内耳分布的良好的荧光探针，可用来检测庆大霉素的药代动力学和聚集机制．     

Low-dose intratympanic gentamicin treatment of Meniere's disease

To control attacks of vertigo while preserving both hearing and labyrinthine function, low doses of gentamicin were instilled intratympanically in nine patients with intractable unilateral Meniere's disease. Each patient received six instillations of antibiotic of 4 mg each (total dose, 24 mg). Patients were then followed for 2–4 years. Long-term results of treatment are reported according to the American Academy of Otolaryngology-Head and Neck Surgery 1985 criteria. Of the nine cases, three experienced complete control of vertiginous attacks, while six received substantial control. Post-treatment hearing acuity was unaffected, although disability following treatment became worse in one patient, a 66-year-old man. Caloric responses after therapy were absent or severely reduced in three ears, moderately reduced in two ears and unchanged in four ears. In three patients, labyrinthine function was found damaged 4–8 days after administration of the last dose of drug. Overall, intratympanic instillations of low doses of gentamicin in patients with intractable Meniere's disease were found to control vertiginous attacks with less damage to the inner ear function than that reported in the literature.     

Low-dose intratympanic gentamicin treatment of Meniere's disease

To control attacks of vertigo while preserving both hearing and labyrinthine function, low doses of gentamicin were instilled intratympanically in nine patients with intractable unilateral Meniere's disease. Each patient received six instillations of antibiotic of 4 mg each (total dose, 24 mg). Patients were then followed for 2–4 years. Long-term results of treatment are reported according to the American Academy of Otolaryngology-Head and Neck Surgery 1985 criteria. Of the nine cases, three experienced complete control of vertiginous attacks, while six received substantial control. Post-treatment hearing acuity was unaffected, although disability following treatment became worse in one patient, a 66-year-old man. Caloric responses after therapy were absent or severely reduced in three ears, moderately reduced in two ears and unchanged in four ears. In three patients, labyrinthine function was found damaged 4–8 days after administration of the last dose of drug. Overall, intratympanic instillations of low doses of gentamicin in patients with intractable Meniere's disease were found to control vertiginous attacks with less damage to the inner ear function than that reported in the literature.     

Hearing loss following intratympanic instillation of gentamicin for the treatment of unilateral Meniere's disease

OBJECTIVE: To determine the incidence, extent, and time course of hearing loss following instillation of intratympanic gentamicin using a predetermined fixed protocol for incapacitating unilateral Meniere's disease and to determine whether such loss is associated with any identifiable risk factors. STUDY DESIGN: A retrospective analysis of all patients treated with intratympanic gentamicin between 1988 and 1998 using American Academy of Otolaryngology-Head and Neck Surgery reporting guidelines (1985 and 1995). A predetermined regimen using a fixed dose (gentamicin 26.7 mg/mL administered three times daily for 4 consecutive days) was used. METHODS: The records of patients treated with this particular protocol were reviewed. The relationship between pretreatment hearing acuity, pretreatment bithermal caloric response, duration of symptoms, and previous treatment to post-treatment hearing were analyzed with respect to hearing. RESULTS: Complete vestibular and audiologic data over a minimum 2-year follow-up were available for 85 individuals. Sixty-three patients (74.1%) had unchanged or improved hearing, and 22 patients (25.9%) realized hearing loss. In 80% of the latter, it occurred during the first month post-treatment. When hearing acuity at the 1-month post-treatment interval remained unchanged (91.1%), it was likely to remain so over the next 23 months. A significantly higher incidence of profound hearing loss was noted in patients who developed hearing loss in the first month, as compared with those who developed hearing loss at a later period (p = .0207, relative risk = 1.5). Re-treatment was not associated with hearing loss. The only identifiable risk factor for developing hearing loss was pretreatment hearing acuity stages 3 and 4 (pure-tone average > 40 dB) (p = .022, relative risk = 1.5). CONCLUSION: Hearing loss is a recognized complication of treatment with intratympanic gentamicin, occurring in approximately 26% of individuals. In those individuals in whom hearing acuity has remained unchanged after the first month interval, significant worsening of hearing is unlikely, and patients can be reassured accordingly.     

Systematic review of intratympanic gentamicin in Meniere's disease

OBJECTIVES: To assess and summarize the best available evidence for the use of intratympanic gentamicin in patients with Meniere's disease with respect to improvement of vertigo, tinnitus, and change in hearing. METHODS: Comprehensive electronic searches were conducted on the databases of MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials. All generated titles were reviewed, and potentially relevant articles were assessed for inclusion. Data from included articles were extracted and summarized. RESULTS: Overall pooled results on vertigo control revealed complete or substantial control in 89% of patients (study range 73-100%). Hearing was worsened in 26% (0-90%). Subjective improvement in tinnitus was seen in 57% of patients (0-82%). Different treatment protocols all resulted in similar rates of vertigo control. CONCLUSIONS: Intratympanic gentamicin appears effective in controlling the symptoms of Meniere's disease, regardless of the protocol used. Although the literature on this treatment is extensive, there is a likelihood of significant bias in many currently published reports. There is a clear need for a prospective, randomized, blinded, placebo-controlled trial to assess the true effectiveness of this treatment.     

Effects of a single intratympanic gentamicin injection on Meniere's disease

CONCLUSION: Both single and multiple injections of ITGM were effective in vertigo control and functional improvement. However, the risk of sensorineural hearing loss was much lower for a single injection than for multiple injections. OBJECTIVES: While intratympanic gentamicin injection (ITGM) has been established as treatment option for intractable Meniere's disease, several injection protocols have been introduced. The risk of sensorineural hearing loss (SNHL) has been reported to be variable for each protocol. Among the protocols, the single injection protocol is an easy to administer, well-tolerated and cost effective technique, as compared with others. We compared the clinical efficacy of ITGM with regard to the vertigo control rate and the incidence of SNHL between two different protocols: the use of single and multiple injections. MATERIALS AND METHODS: A retrospective review was conducted for 30 subjects who were treated with ITGM with intractable unilateral Meniere's disease from May 1997 through February 2005. The patients were divided into two groups according to the protocol utilized: the multiple injection group (n =10) and the single injection group (n =20). Treatment efficacy was evaluated by using the AAO-HNS Committee on Hearing and Equilibrium guidelines (1995). RESULTS: Effective vertigo control (Class A and B) were accomplished in 90% of patients in the multiple injection group and in 90% of patients in the single injection group. Functional status was also markedly improved in both groups. However, a significant hearing loss occurred more frequently in the multiple injection group (71%) than in the single injection group (5%). The rate of caloric loss was not different for the two groups (88% for the multiple injection group vs. 85% for the single injection group).     

Effect of intratympanic gentamicin on hearing and tinnitus in Meniere's disease.

OBJECTIVE: The objective of this study was to examine the effect of intratympanically applied gentamicin (GM) (30 mg/mL) on hearing and tinnitus in patients with intractable Meniere's disease. STUDY DESIGN: A prospective study was conducted on 93 subjects treated with intratympanically applied GM. The mean pure-tone average (PTA) at speech frequencies was measured before the treatment and after 2 weeks, 1 month, 3 months, 6 months, 1 year, and 2 years after injections. Tinnitus was surveyed with a questionnaire. The mean duration of Meniere's disease was 9.8 years (range, 1-33 years). PATIENTS: The study group consisted of 28 men and 65 women. The mean age was 50.9 years (range, 19-74 years). RESULTS: The mean PTA at speech frequencies for the group worsened from 60 dB to 68 dB, which was statistically significant. Ten ears were deafened. The mean tinnitus handicap score before treatment was 2.92; 2 years after treatment, it was 2.26, indicating significant abatement of tinnitus during the course of the treatment. CONCLUSIONS: The authors found that the average frequency of deafening was 10% and it was dose dependent. GM caused alleviation of tinnitus in the majority of the patients.     

Histopathology of the vestibular end organs after intratympanic gentamicin failure for Meniere's disease

CONCLUSION: To our knowledge, this is the first report of the histopathology of the vestibular end organs following intratympanic gentamicin for intractable Meniere's disease. There was relative sparing of the utricular macula, compared with the cristae ampullares. However, the utricular macula exhibited severe hair cell loss. Clinically, the patient has been free from vertigo spells for 3 years following labyrinthectomy. Objective: To describe the histopathology and morphometry of the vestibular end organs from a 59-year-old Meniere's patient who underwent transmastoid labyrinthectomy for recurrent vertigo after failed intratympanic gentamicin. MATERIALS AND METHODS: Light and transmission electron microscopy were utilized; with unbiased stereology-physical fractionator for type I, type II hair cell, and supporting cell counts. Comparison with end organ histopathology in a 56-year-old with Meniere's disease without gentamicin treatment was carried out. RESULTS: Histopathological analysis of the semicircular canal cristae ampullares showed severe atrophy of the neuroepithelium with undifferentiated cells, and fibrosis and edema of the stroma. The utricular macula had some remaining type I and type II vestibular hair cells, and nerve fibers and terminals within the underlying stroma. Morphometric measures were obtained from the utricular macula: 2000 type I and 500 type II hair cells, representing 7.3% of type I hair cells and 4.9% of type II hair cells compared with normative controls, and 24 000 supporting cells were obtained.     

小剂量庆大霉素鼓室内注射治疗难治性梅尼埃病眩晕的临床研究

目的：分析小剂量庆大霉素鼓室内注射治疗难治性梅尼埃病眩晕的疗效。方法：19例单侧难治性梅尼埃病患者显微镜下鼓室内注射庆大霉素,根据床旁试验（自发性眼震、摇头实验、甩头试验）,听力变化或患者主观症状来决定3周后是否需要再次注射。结果：19例患者中17例眩晕能得到控制,眩晕控制率89％,其中5例患者经1次注射后眩晕就得到控制;8例患者2次注射后眩晕达到控制,其中1例患者因不能忍受耳内肿胀感,要求进一步治疗,行内淋巴囊减压后,症状缓减;有4例患者经3次注射后眩晕得到控制;另外2例患者注射2次后眩晕无改善,要求终止治疗。2例患者注射后听力好转,14例患者注射后听力无变化,3例患者（15％）注射后听力进一步下降。结论：运用小剂量鼓室内庆大霉素注射治疗难治性梅尼埃病眩晕,1次注射后观察3周决定再次注射的必要性,结果显示这一治疗方案既能有效控制眩晕的发作,又能降低听力损伤的风险。     

Factors relating to the vertigo control and hearing changes following intratympanic gentamicin for intractable Ménière's disease.

OBJECTIVE: To look for factors relating to the vertigo control and hearing changes after intratympanic injections of gentamicin (GM). STUDY DESIGN: Prospective. SETTING: Tertiary referral medical center. PATIENTS: Twenty-eight patients with intractable Ménière's disease. INTERVENTIONS: Three intratympanic injections of GM (once per day for three consecutive days). MAIN OUTCOME MEASURES: Although five patients needed further GM injections or vestibular neurectomy because of poor control (Group I), 23 patients had their vertigo controlled for more than two years without further treatment (Group II). The number of vertigo spells per month, pure-tone audiometry, electrocochleography, caloric response, post-head shake nystagmus, and plasma vasopressin as a stress marker were examined. RESULTS: Before GM injections, there was no difference in the number of vertigo spells per month between Groups I and II. However, the hearing thresholds were higher in Group I. Hearing improvement, increase in percentage of canal paresis and induction of post-head shake nystagmus were observed after GM injections only in Group II. Even in the 11 patients who showed an improvement in hearing of more than 10 dB (hearing improvement group), percentage of canal paresis was increased after GM. More, premedication plasma vasopressin levels were lower in the hearing improvement group as compared with the hearing loss/no changes group. Four of eight patients became negative for dominant negative summating potential in electrocochleography after GM injections in the hearing improvement group. CONCLUSION: Our data indicate that the frequency of vertigo is not a key factor in the vertigo control after GM injections, that induction of vestibular damage in the injected ear is essential for the control of vertigo and this effect is mostly pronounced in patients with milder hearing loss, and that hearing improvement is not only a consequence of good vertigo control but also affected by the stress level before treatment.     

Recovery of subjective visual horizontal after unilateral vestibular deafferentation by intratympanic instillation of gentamicin

The time course of the recovery of subjective visual horizontal (SVH) after unilateral vestibular deafferentation by intratympanic instillation of gentamicin was studied. Six patients who underwent intratympanic gentamicin instillation therapy for Meniere's disease (1 man and 5 women, 32 to 69 years of age) were enrolled in this study. For comparison, SVH in 23 healthy subjects (12 men and 11 woman, 23 to 48 years of age) was also measured. The mean +/- SD of SVH in healthy subjects was 0.0 +/- 1.1 deg. All of the 6 patients showed significantly deviated SVH toward the injected side-down at the early stage after the therapy. Although one patient showed recovery of SVH to the normal range 25 days after the injection, the other patients required more time for recovery. Three patients did not show recovery to the normal range after 1 year. On the other hand, spontaneous nystagmus observed using an infrared CCD camera in total dark disappeared after 35 days (median). Patients who had normal vestibular evoked myogenic potentials before the therapy showed a tendency of delay of recovery of SVH. The reasons why the recovery of SVH took longer than the disappearance of spontaneous nystagmus are discussed in this report.