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Abnormalities of the Stapedius Reflex Responses in Patients with Vestibular Neuronitis

R. Yagiz, A. Tas, C. Uzun, M. Adali, M. Koten, I. Adali, A. Karasalihoglu

Department of Otorhinolaryngology, Faculty of Medicine, Trakya University, Edirne, Turkey

ABSTRACT

Objective: The aim of this study was to evaluate the stapedius reflex responses in patients with vestibular neuronitis.
Study design: This study was designed as a prospective clinical study.
Setting: The study was performed in the Department of Otorhinolaryngology, Faculty of Medicine, Trakya University, Edirne, Turkey.
Patients: The study was carried out in 18 patients with vestibular neuronitis.
Interventions: All patients were investigated with audiological tests in the acute phase, after 1 and 3 months.
Main outcome measures: The audiological tests performed were pure tone audiometry, tympanometry, auditory brainstem response and stapedius reflex responses (threshold, latency, amplitude and reflex decay).
Results: Elevated stapedius reflex thresholds were obtained bilaterally in four of the 18 patients in the early disease phase. Between healthy and affected sides, mean stapedius reflex latency values of the patients were significantly different at the measurements both at the onset of disease (p<0.05) and 1 month after the onset (p<0.05). Ten of the 18 patients had prolonged reflex latency values on affected side in the early disease phase. Six of the 18 patients had decreased reflex amplitude value on the affected side. Five of the 18 patients had both prolonged latencies and decreased amplitudes. The abnormal reflex decay was not recorded in any of the 18 patients.
Conclusions: Our findings, which indicated abnormalities of stapedius reflex responses in patients with vestibular neuronitis, may support that stapedius reflex arch or its medullary connections could be affected by vestibular neuronitis.
Key words: Vestibular neuronitis, Acoustic reflex, Impedance audiometry.
Pro Otology 2-3: 102-105, 2003

Introduction

Vestibular neuronitis is a common cause of peripheral vestibular vertigo. It is characterised by a sudden onset of severe rotational vertigo and a marked unilateral loss of vestibular function on the affected side. There are no associated auditory or neurological symptoms. The vertiginous episode gradually resolves over days and recurrence is uncommon (1,2).

The aim of the present study was to evaluate the stapedius reflex responses in patients with vestibular neuronitis.

Materials and Methods

The study was carried out in 18 patients with vestibular neuronitis, who admitted to our department in the early phase of the disease, between December 1999 and April 2003. The patients consisted of 8 males and 10 females. The mean age was 50 years (range: 17-69 years). The patients, who had conductive or sensorineural hearing loss and abnormal tympanogram were not included into the study. Oto-neurological examination was also performed in all patients. Diagnosis of the vestibular neuronitis was based on the following criteria (3,4): I- sudden onset of vertigo continuing for more than 24 hours, II- no associated auditory system symptoms, III- reduced or absent caloric response on the affected side, and IV- no neurological finding indicating a disorder of the central nervous system. Eighteen healthy subjects consisted the control group. The control group was selected from subjects who had no history of previous vestibular or neurological disease. There were no differences between the vestibular neuronitis and the control group in relation to age and sex (p<0.05). All patients were investigated with audiological tests in the acute phase and with caloric tests within one week after onset. These tests were re-performed after 1 and 3 months.

The audiological tests performed were pure tone audiometry, tympanometry, auditory brainstem response (ABR) and stapedius reflex responses (threshold, latency, amplitude and reflex decay). Pure tone audiometry, tympanometry, stapedius reflex responses were also studied in the control group. Pure tone audiometry (with digital clinical audiometer model AC3 Interacoustics, Assens, Denmark) and ABR (with Danplex BRA2 Analyser) were performed. The stapedius reflex responses were measured with the impedance audiometer model AZ7-Interacoustics and its XYT recorder model AG3.

The stapedius reflex thresholds (SRT) were established at 1000 Hz with the contralateral stimulus. The maximum intensity used was 110 dB HL. Elevated reflex thresholds were considered when the reflex response is not present at 95 dB HL. This level was considered as the level of elevation because it has been reported that elevation of reflex threshold over 95 dB may support retrocochlear lesions (5).

Test stimuli for the stapedius reflex latency procedure were presented at 10 dB above the reflex threshold level. The stapedius reflex latency (SRL) measurements were taken from the onset of the signal to the first detachable increase in acoustic impedance (6,7), and were calculated as 1 mm = 5 ms depending on scale of the chart.

The stapedius reflex amplitude (SRA) was defined as the difference between baseline and the maximum amplitude of the curve (7), and was calculated as 5 mm = 0.25 ml depending on scale of the chart.

Abnormal reflex decay was defined as decline to half-life, less than 50% of the maximum impedance change, within 5 seconds of stimulus onset (6).

The bithermal caloric test (37 +/- 7) was performed by Hallpike’s method using Chartr water caloric stimulator NCI-480 (ICS medical). A caloric side difference by 20% or more was considered pathological.

The results were analysed by the Independent-samples t-test and Paired-samples t-test statistical methods.

Results

Table 1. The distribution of patients according to sex and affected side.

The distribution of patients according to age and sex in the early phase of vestibular neuronitis is illustrated in FIG.  1. The distribution of patients according to sex and affected side is shown in the Table 1.

The stapedius reflex thresholds for both ears of all patients were obtained in the early disease phase. The elevated reflex thresholds were obtained bilaterally in four (22.2 %) of the 18 patients at 100 dB HL stimuli intensity. After 3 months from onset, all of these patients had bilaterally stapedius reflex thresholds at 85-90 dB HL stimuli intensity.

Mean latency values of the patients with vestibular neuronitis were 145.2 ms on affected side, and 128.7 ms on healthy side at the onset phase of the disease. In the follow-up observations at 1 and 3 months after the onset, mean latency values were 144.4 ms and 139.1 ms on affected side, and 128 ms and 126 ms on healthy side, respectively. Mean latency values of the control subjects were 129.7 ms in right ears and 129.3 ms in left ears (FIG. 2) in the control group.

 

FIG 1. Age-sex distribution of patients with vestibular neuronitis.
 

FIG 2. Mean latencies of stapedius reflexes in the patients with vestibular neuronitis and control group.

 

We used Independent-samples t-test to compare mean latency values of healthy and affected sides. We found significant differences at the measurements both at the onset of disease (p<0.05) and 1 month after the onset (p<0.05) between healthy and affected sides. Differences were not statistically significant 3 months after the onset. Also, we used Paired-samples t-test to compare mean latency values in the same sides according to observation periods. These comparisons did not show statistically significant differences. These findings have shown that latency values had tendency to recover, however they did not recover.

Interaural latency differences (ILD) were also calculated for each individual in each group. The mean ILD were 21.5 ms in the early disease phase and 8.8 ms in the control group. Comparison of the two groups produced statistically significant difference (p<0.008) (FIG. 3).

The 99% confidence limit for mean normal ILD was used as upper limit of the normal range. This upper limit value was 15.5 ms. Ten of the 18 patients had prolonged reflex latency values on affected sides. In 4 of these 10 patients, latency values were recovered 3 moths after the onset. Four patients, who had elevated reflex thresholds, had simultaneously prolonged latency values on the affected side in the early disease phase. The latency value of one of the patients with elevated reflex thresholds recovered three months after the onset.

Mean values of the reflex amplitude in the patients and the control group are shown in the Figure 4. There was no statistically difference between healthy and affected side in both onset and observations periods. However, there was significant difference between the two groups regarding the interaural amplitude differences (IAD) (p<0.05).

 

FIG 3. Mean interaural latency differences in the patients with vestibular neuronitis and control group.
 

FIG 4. Mean reflex amplitude values in the patients with vestibular neuronitis and control group.

 

The 99% confidence limit for mean normal IAD was used as upper limit of the normal range. This upper limit value was 0.27 ml. Six of the 18 patients had decreased reflex amplitude values on the affected side. In four of these 6 patients, amplitude values recovered 3 months after onset. Five of the 18 patients had both prolonged latencies and decreased amplitudes.

The abnormal reflex decay was not recorded in any of the 18 patients. In all patients, ABR showed normal wave form and normal latencies.

Discussion

There are controversies over the etiology and the site of lesion in vestibular neuronitis. Baloh et al. (8) reported degeneration in the vestibular nerve and vestibular end organ cells, and a significant decrease in synaptophysin density in the vestibular nuclei on affected side in a patient with vestibular neuronitis. It was shown in clinical studies that vestibular neuronitis could also affect the brainstem and auditory system (9-11).

The stapedius reflex responses are routinely used in “site of lesion” testing battery to distinguish cochlear lesions from retrocochlear or central ones. Some studies have reported that retrocochlear lesions involving the VIIIth nerve affects responses of the stapedius reflex (6,11). Lehrer and Poole (10) have reported that abnormalities of the stapedius reflex can be found in patients with vertigo. Bergenius and Borg (11) have reported that stapedius reflex threshold elevation can be observed in normal hearing patients with vestibular neuronitis. Also, it has been reported that patients with elevated reflex thresholds have a tendency towards slower recovery of the caloric reaction than patients with normal reflex thresholds (11,12).

The findings of the present study showed that abnormalities of the stapedius reflex responses could be recorded in patients with vestibular neuronitis. We found bilaterally elevated reflex thresholds in 22.2% of the patients with vestibular neuronitis. After 3 months from the onset of the disease, all of these patients had bilaterally stapedius reflex thresholds at 85-90 dB HL stimuli intensity.

It has been reported that elevated or absence reflex thresholds usually recover when the vertigo resolves (10,11). We found prolonged latencies and reductions in amplitude on the affected side of the patients with vestibular neuronitis. However, prolonged latency values partially recovered 3 moths after onset of the disease. Our study has supported that stapedius reflex arch or its medullary connections could be affected by vestibular neuronitis.

In conclusion; our findings, which indicated abnormalities of stapedius reflex responses in patients with vestibular neuronitis, may support the hypothesis that the site of lesion of this disease is the vestibular nuclei on the affected side.

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