Objective: To support the hypothesis that the symptom complex known as visual vestibular mismatch (VVM) can be induced by peripheral vestibular disease.
Design: Retrospective chart review; prospective questionnaire.
Setting: A tertiary/quaternary care hospital clinic.
Methods: The charts of 28 patients who were treated for Ménière's disease were studied. Their responses to a pretreatment VVM questionnaire were scored and compared with their answers in a telephone follow-up to the same questions post-treatment. These questionnaires were compared with those filled in by 100 control patients without ear disease.
Main Outcome Measures: Patients' responses to a VVM-specific questionnaire.
Results: Seventeen of 28 patients had VVM. Gentamicin therapy increased the number of positive answers. There was no correlation between the development of VVM complaints, caloric scores, and posturography performance. No control patients had symptoms of VVM.
Conclusion: We conclude that the development of VVM indicates the onset or worsening of vestibular disease as it can be induced or exacerbated by gentamicin therapy. As there is no correlation between VVM and caloric scores, we suggest that otolithic damage may be responsible for this symptom set developing.
KEYWORDS: gentamicin, Ménière's disease, motion sickness, posturography
The well-known vestibular symptoms in Ménière's disease can often be disruptive to a patient's lifestyle. Patients suffering such recurrent attacks can now be offered the simple but effective therapy of intratympanic gentamicin instillation. After ablation therapy, they no longer suffer the consequences of dramatic fluctuation of labyrinthine function, thus ending the recurrent and unpredictable dizzy spells accompanied by nausea and vomiting. They are then left with the challenge of compensating for their newly created labyrinthine deficit. This is usually successful, with a return to a satisfactory lifestyle.
Patients with classic Ménière's disease usually do not present a diagnostic challenge. Vertigo, nausea, and imbalance are easily definable as being of vestibular origin, with caloric testing often being able to lateralize the lesion. In recent years, more subtle symptoms of vestibular disease have been recognized and are now understood to a larger extent. This subtle symptom set was described as “visual vertigo” by Bronstein (1) and referred to as “visual vestibular mismatch” (VVM) by Longridge and Mallinson (2-4). These symptoms, which were often previously ascribed to a neurologic, histrionic, or psychiatric origin, are now accepted as arising from the vestibular system (1,2). They often present in a subtle fashion, sometimes only during a careful history taking. Recent literature supports the fact that the symptoms are genuine and not at all suggestive of malingering or psychiatric behaviour (1,5-7).
Visual vestibular mismatch is a syndrome in which visual and vestibular information does not mesh satisfactorily in the brain, often resulting in general malaise and complaints that are often vocalized as “dizziness.” This discongruency between the normal environmental signals results in a subset of symptomatology, for example, feeling unwell when walking down the aisle of a supermarket, standing at a busy crosswalk with many cars going by, or in a busy shopping mall. This results from over-reliance on visual signals, which can cause the illusion of movement. Patients can also be bothered by elevator rides, escalator rides, walking across checkered floors, and awareness of dislike of fluorescent lights. Frequently, there is an awareness of new onset of motion sickness not present prior to the instigating event, and this is also accepted as a symptom of newly developed vestibular pathology (2). Other complaints attributable to VVM are described occasionally. Symptomatology can be invoked by leafed boughs of trees waving up and down, Venetian blinds swaying, or moving water (such as rippling on the water of the seashore or even in a hand basin). Symptoms very often also include nausea. These symptoms have been described previously as being related to mismatch between visual and vestibular signals (4,5,8,9).
Visual vestibular mismatch is a clinical diagnosis. Often it coincides with an abnormality involving the balance system that can be detected by Computerized Dynamic Posturography (CDP). In one study, CDP results were abnormal in approximately two-thirds of patients with VVM caused by trauma, although in about one-third of patients, the symptoms were present without abnormality on posturography (4).
In a study to assess the effectiveness of intratympanic gentamicin treatment on unilateral Ménière's disease (10), patients were assessed by telephone follow-up. During this follow-up, several patients spontaneously voiced complaints of VVM. This was followed up in more detail by a repeat telephone call to clarify VVM symptoms pre and post intratympanic gentamicin. Patients treated with gentamicin for Ménière's disease over a period of 4 years were assessed for VVM, and these findings are the basis of this article. The objective of the investigation was to determine whether a purely peripheral vestibular disorder could produce VVM and whether alteration of peripheral function resulted in the development of or a change in VVM symptoms.
PATIENTS AND METHODS
A retrospective chart review of patients treated with intratympanic gentamicin was undertaken (10). During telephone follow-up to determine the success or failure of intratympanic gentamicin, a questionnaire (Table 1) was given to each patient to determine whether he or she had experienced dizziness induced by eight situations and whether he or she had motion sickness. These complaints were separate from the dizziness occurring during the acute vertiginous episodes of their Ménière's disease. Patients were asked whether these symptoms had been present before or after intratympanic gentamicin therapy and, if present before, whether they were changed by the therapy for better or worse. One hundred patients with no audiovestibular abnormalities, referred for nose and throat disease, were used as controls.
All of the 28 patients completed our questionnaire (see Table 1), both prior to and after their intratympanic gentamicin therapy. Eleven were not bothered by any of the stimuli inquired about and gave “no” answers to all nine questions both pre- and post-treatment.
In Table 2, it can be seen that 27 answers suggested a worsening of symptoms (i.e., induced or brought on) and 16 answers suggested an improvement of symptoms. But of these 16 symptom improvements, 10 still suggested lingering symptoms (i.e., answers were still positive but less so). This suggests that intratympanic gentamicin therapy is not a good modality for resolving the symptoms of VVM. On the other hand, for 26 of the 27 worsening of symptoms answers, the symptoms arose de nouveau, suggesting that intratympanic gentamicin therapy is, in fact, an agent highly suspicious of inducing symptoms of VVM.
Table 1. Dizziness Questionnaire
- Does walking down a supermarket aisle increase your dizziness?
- Because of your dizziness do you have difficulty reading?
- Do you have motion sickness?
- Do fluorescent lights make your dizziness worse?
- Does standing at the edge of a busy crosswalk make your dizziness worse?
- Does your dizziness get worse in a shopping mall?
- Does your dizziness get worse on an escalator?
- Does your dizziness get worse in an elevator?
- Do checkered floors make your dizziness worse?
(Four visual vestibular mismatch questions bolded for this article only.)
Table 2. Effects of Intratympanic Gentamicin on Visual Vestibular Mismatch*
|Good Outcome (cured/improved)||3||1||1||2||2||2||0||3||2||16|
|Poor outcome (induced/worsened)||6||0||3||3||1||7||3||0||4||27|
|Total in which change occurred||9||1||3||5||3||9||3||3||6||43|
* Number of changed responses to questionnaire pre- and post-treatment.
** See Table 1.
Improved = symptoms present but more tolerable after treatment
Worsened = symptoms present but less tolerable after treatment
Induced = symptoms developed after treatment
Cured = symptoms disappeared after treatment.
Table 3. Number of Patients with Positive Answers to Each Question Pre and Post Intratympanic Gentamicin Therapy (N = 28)
* See Table 1.
** Visual vestibular mismatch-specific questions.
ITG = intratympanic gentamicin
All of the patients underwent our standard protocol (discussed elsewhere (10)) with pre and post CDP and caloric assessment. The caloric changes, CDP changes, and treatment outcomes are not reported here as they are not related to this study, but there was no correlation in any of these parameters between the results of the 11 negative responders and the 17 others with one or more positive complaints.
In the 17 patients who had any positive answers at all, supermarket aisles, shopping malls, and checkered floors were the most common inducers of these complaints (questions 1, 6, and 9). Surprisingly, fluorescent lights were also complained of commonly. We also regard these four questions (1, 4, 6, and 9) as being the most indicative of VVM as they all assess similar circumstances; they all ask about maintenance of balance in the presence of an active disorienting visual stimulus. As a result, we examined these four VVM-specific questions (bolded in the questionnaire by us for the purpose of this article) more closely, hypothesizing that difficulties with VVM would be reflected when a patient was placed in such circumstances.
Of the 17 patients who responded positively to any of the questions in the questionnaire, 10 of them had an answer change to at least one of the four VVM-specific questions post therapy. This is summarized in Table 3. There were a total of 24 “changed” answers (i.e., “yes” to “no” or “no” to “yes”). Table 4 examines the VVM-specific questions. In this category, there were 20 post- treatment answers suggesting development of symptoms and 4 indicating resolution of symptoms. Control patients did not answer the questionnaire positively.
The complaints of patients with VVM have been described by us previously (2- 4). The exact anatomic location causing the symptoms is unclear (11). The association with head injury may suggest origins in the neck, brainstem, cerebellum, or inner ear (4).
Our patients with Ménière's disease stand as a model of specific inner ear damage as a result of their gentamicin injections. The development and alteration of symptoms of VVM with therapy for Ménière's disease indicate that pure inner ear disease can induce symptoms characteristic of VVM in the absence of any other factors. We realize that although it is possible that patients' symptoms may have developed because of the passage of time and not because of their intratympanic gentamicin therapy, the patients who did note changes specifically felt that the changes coincided with the gentamicin treatments. We consider this to be proof that the gentamicin induced these complaints. It is not known whether these symptoms would be totally or even partially relieved by complete ablation of the inner ear. To date, no patient has had symptoms severe enough to justify surgical ablation. This procedure would result in complete destruction of inner ear function, which would then allow determination of whether the symptoms of VVM are relieved. At some point, this information may become available.
The absence of a close correlation between caloric response and relief of symptoms of vertigo suggests that damage to the lateral semicircular canal may not be the sole cause of the change. The initial and most extensive hair cell damage in aminoglycoside ototoxicity occurs in the apex of the cristae and striolar regions of the maculae, and gentamicin has also been implicated in otoconial membrane damage (12). We hypothesize that some patients also suffer some decreased function of the otoliths resulting from therapy for their Ménière's disease and that the otolithic damage may be responsible for the development of VVM. The amount of damage caused by the gentamicin to the inner ear structures already damaged by Ménière's disease may explain why some of our patients have improvement in and others have worsening of their symptoms.
As none of the control patients had dizziness in the first place, a direct comparison of responses to the questions cannot be made. The questions to the control group had to be phrased differently, that is, “Do you get dizzy in a shopping mall?” This presented a different situation than the questions asked of the patients with Ménière's disease, which took the form of “Does your dizziness change in a shopping mall?” In the control group, 15% suffered from motion sickness and always had.
We are unaware of any effective method of improving the symptoms of VVM once they are present. Generally, patients are instructed to undertake the maximum activity they can tolerate to try and suppress their symptoms as effectively as possible. By challenging the balance and visual systems, it is felt that this may improve the integration of signals so that the symptoms of this syndrome are relieved. Unfortunately, in our experience, this is frequently not the case, and some patients find that their symptoms are worsened by this mobilizing approach. Some patients have these symptoms on a long-term basis, and we are concerned that they may be present permanently.
Table 4. Visual Vestibular Mismatch Specific Question Changes Post Therapy
|Patients in whom symptoms developed||6||3||7||4|
|Patients in whom symptoms resolved||2||0||1||1|
* See Table 1.
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