Murray, Katherine J. PhD; Hill, Keith PhD; Phillips, Bev PhD; Waterston, John MD, FRACP
Vestibular rehabilitation (VR) is an exercise-based approach to the treatment of individuals with vestibular dysfunction. Individuals with vestibular dysfunction are generally considered appropriate for a program of VR if they have symptoms of motion-provoked dizziness and balance dysfunction. By using these criteria, VR has been shown to be an effective treatment strategy.1 Success rates vary, however, and authors have questioned whether VR is the optimal treatment approach for all individuals with vestibular dysfunction.2 It is possible that different treatment strategies are necessary for different types of vestibular mechanism involvement. Although the peripheral vestibular apparatus consists of semicircular canal and otolith structures, it is only recently that tests have been developed to measure otolith function.3 In conjunction with traditional tests of horizontal semicircular canal function (caloric testing), these tests provide further information regarding the extent of vestibular pathology.
It remains unknown, however, whether involvement of the otolith organs of the inner ear (the utricle and saccule) influences an individual's response to rehabilitation. Most studies that have reported the effectiveness of VR in treating individuals with vestibular dysfunction have advocated its use regardless of the extent of inner ear involvement.4 This is despite the suggestion that additional otolith dysfunction is indicative of a more severe and extensive vestibular lesion,5–7 which may be less responsive to rehabilitation. However, a recent study identified that additional otolith dysfunction did not influence the clinical presentation of individuals with a diagnosed vestibular lesion.8 The aim of this study was to build on this previous work and to identify whether additional otolith dysfunction influences the response to rehabilitation of patients with a diagnosed peripheral vestibular disorder. It was hypothesized that otolith organ involvement would adversely influence rehabilitation outcomes.
Participants were recruited from the Audiology Departments of the Alfred and the Royal Victorian Eye and Ear Hospitals in Melbourne, Australia. A total of 47 participants were recruited for the study (26 men, 21 women). The mean age of the full sample was 55.7 years (standard deviation = 14.5, range = 24-81). Based on vestibular function test results (described below), there were 18 participants (38%) with an isolated unilateral loss of semicircular canal function only and 29 participants (62%) with a combined unilateral loss of semicircular canal and otolith organ function. For participants with a combined lesion, 41.4% had additional utricular involvement only (n = 12), 41.4% had additional saccular involvement only (n = 12), and 17.2% had impaired function of both otolith organs (n = 5).
All participants received a full battery of vestibular function tests. Bithermal caloric testing was used to assess horizontal semicircular canal function. Static bias and vestibular-evoked myogenic potential (VEMP) testing were used to assess otolith organ function. Participants were included in the study if they could be categorized as having either:
1. An isolated unilateral loss of semicircular canal function only, as characterized by
a. more than a 25% difference between left-sided and right-sided semicircular canal responses demonstrated on caloric testing (ie, degree of canal hypofunction on affected side >25%, where 100% indicates a complete loss of function) and
b. normal otolith function test results, or
2. A combined unilateral loss of semicircular canal and otolith organ function, as characterized by
a. more than a 25% difference between left-sided and right-sided semicircular canal responses demonstrated on caloric testing and either:
b. abnormal static bias test results (an assessment of utricular function). This test involves setting a dimly illuminated light bar to earth horizontal in the absence of visual cues.9,10 An average deviation of the subjective visual horizontal greater than 3° from horizontal is considered to be abnormal, and/or
c. abnormal VEMP test results (an assessment of saccular function). This test involves the unilateral delivery of loud monaural clicks and the subsequent measurement of responses via skin electrodes on the tonically contracted, ipsilateral sternocleidomastoid muscle.11,12 An amplitude ratio between left-sided and right-sided responses greater than 3:1 was considered to be abnormal, so that the side with the smallest amplitude was considered impaired.
Participants were also required to be appropriate for a program of VR, with criteria including a history of positional and/or motion-provoked symptoms,13 a history of impaired balance,13 and reports of substantial limitations in activities of daily living.14
Participants were not considered appropriate for the study if they were younger than 18 years of age, had an unstable (fluctuating) vestibular lesion,15 had significant orthopaedic or neurological deficits that influenced balance and mobility performance and prevented reliable completion of the testing procedure, and/or had insufficient English language skills or cognitive ability to provide informed consent or to reliably participate in the testing procedure. The study received approval from the Research and Ethics Committees at the Alfred and the Royal Victorian Eye and Ear Hospitals, and all participants gave written informed consent.
Comprehensive Clinical Assessment at Baseline
After referral to the study, all participants received a comprehensive clinical assessment at the balance testing facility. The physical therapist who performed the assessment (assessing physical therapist) was blinded to the vestibular function test results until the study had been completed.
A detailed history of the current vestibular problem was documented including time since onset of vestibular dysfunction (months), use of medications, current symptoms, and functional limitations (subjective reports of problems with driving and work).
Vestibular Symptom Index: Levels of symptom severity were measured using the Vestibular Symptom Index (VSI).16 The VSI consists of 6 items (impaired balance, dizziness, vertigo, nausea, visual sensitivity, and headache), which are rated on a scale of 0 to 10, with 0 indicating absence of the symptom and 10 indicating perception of the greatest possible severity. A total score (out of a maximum possible score of 60) is calculated as a sum of the individual scores for each item.
Dizziness Handicap Inventory: Levels of self-perceived handicap were evaluated using the Dizziness Handicap Inventory (DHI).17 The DHI consists of 25 items, which are marked with “yes” (4 points), “sometimes” (2 points), or “no” (0 points). A total score is calculated out of 100, with higher scores indicating a higher level of self-perceived handicap. Individual scores are also calculated for each of the 3 subscales (functional, emotional, and physical).
Human Activity Profile: Levels of physical activity were evaluated using the Human Activity Profile (HAP).18 The HAP consists of 94 common activities, which are rated as “still doing,” “have stopped doing,” or “never did.” An Adjusted Activity Score (AAS) is recorded, which is calculated by subtracting the number of lower number activities marked as “have stopped doing” from the highest numbered activity still being done.
Disability Rating Scale: Levels of self-perceived functional disability were measured using the Disability Rating Scale (DRS).19 The DRS is a 6-point scale (0-5), which ranges from participants having few symptoms and no disability (score = 0) to participants having severe symptoms and long-term disability so that they have been unable to work for more than a year (score = 5).
Balance and gait measures
Step test: Dynamic standing balance was measured using the Step Test.20 The number of times participants could step 1 foot completely on and then off a 7.5-cm block in 15 seconds was recorded. Each leg was tested separately, and performance on the worst side was used for data analysis.
10-m walk test: Usual gait speed was measured using the 10-m walk test.21,22 The performance of this test with head rotation has also been recommended in the assessment of individuals with vestibular pathology because it facilitates the observation of gait deviations and loss of balance in this population.23 Participants were timed walking “at their comfortable walking speed” both with and without head turns and using their customary gait aid, to the end of a 10-m walkway, and a measure of velocity (meters per minute) was calculated.
Tandem walk test: Walking with a reduced base of support was measured using the tandem walk test.24 Participants walked 15 steps along a line on the floor approximately 1.5 cm wide and the number of correct steps was counted. A correct step was defined as a step on the line, with heel to toe not visibly separated. A maximum score of 15 steps was set.
Computerized dynamic posturography: Static standing balance was measured using computerized dynamic posturography (Smart Balance Master system, Neurocom International, Clackamas, OR, 1999). The Sensory Organization Test, consisting of 6 test conditions (eyes open, eyes closed and visual conflict conditions, on a firm surface and a sway referenced surface), was performed according to the published protocol. An equilibrium score (% sway) was calculated for each condition,1–6 ranging from 0% to 100%, where 0% represents a fall and 100% represents complete stability. A total composite score was also calculated by adding the single equilibrium scores for all the trials and dividing the total by 14.
Program of Vestibular Rehabilitation
After completion of the baseline clinical assessment, customized home exercise programs (HEPs) were developed by the assessing physical therapist. These included vestibular adaptation exercises, habituation exercises, balance/gait activities, and general fitness training as required.19 Vestibular adaptation exercises involve head movement while visually fixating on a target and controlled studies have demonstrated the effectiveness of these exercises in improving measures of balance performance in individuals with acute and chronic vestibular dysfunction.25,26 Habituation exercises are based on the concept that repeated exposure to a provocative stimulus will result in a reduction in the symptomatic response to that position or movement,27 and the selection of specific exercises to be included in the HEP was based on the results of the clinical assessment. Habituation exercises have been shown to be effective in improving independence in activities of daily living and in reducing symptoms of dizziness.28 A wide range of balance and gait exercises have been described in the literature to encourage the integration and use of vestibular information for balance.29 These types of exercises have been found to be effective in improving static and dynamic balance performance in individuals with chronic dizziness and balance problems.30 Participants were advised to perform the exercise program 3 times every day and were provided with a home exercise diary to record completion of the program.
Review of Progress
Participants were required to attend the balance testing facility every 1 to 2 weeks for a review of their progress. These review appointments were performed by a physical therapist (treating physical therapist), who was not involved in completing the baseline clinical assessment and who was blind to the diagnostic test results and clinical assessment findings. At each appointment, the treating physical therapist reviewed the HEP and updated it as necessary to reflect individual improvements or difficulties.
Completion of the HEP diary was reviewed and adherence with the exercise program was documented at each review appointment using the Compliance Rating Scale, which is a 4-point scale that ranges from excellent compliance with the HEP (score = 1) to poor compliance (score = 4). At the week 8 reassessment, a total compliance rating score was calculated by adding the individual scores recorded at each review visit and dividing by the total number of review visits.
Reassessment After Completion of VR
After the 8-week treatment period, participants attended the balance testing facility for a reassessment, performed by the assessing physical therapist, of all measures taken at baseline. A score of perceived outcome after the program of VR was obtained from each participant using the Symptom Outcome Score,18,24 a 5-point scale (0-4), which ranges from the patient having no symptoms at the end of rehabilitation (score = 0), to having worse symptoms on a persistent basis relative to the prerehabilitation period (score = 4).
Statistical analyses were performed using SPSS software package (SPSS version 16, SPSS Inc, Chicago, IL). All continuous variables were analyzed for distribution and skew. Because of the number of comparisons being performed, a more conservative level of significance was used, so that P values <.01 were considered to be significant.
Between-group comparisons were made of participants with versus participants without otolith organ involvement. Data were examined for comparability at baseline with respect to demographic factors and clinical parameters. To compare the response to VR of the 2 groups, difference (change) scores were calculated between measures taken at baseline and those taken immediately after completion of VR. For normally distributed variables, paired-sample t tests were used to evaluate the effectiveness of the intervention, and Wilcoxin's signed rank tests were used for non-normally distributed data. To compare the groups, between-group comparisons of the difference (change) scores were used. For normally distributed variables, independent t tests were used and for non-normally distributed variables, Mann-Whitney U tests were used. Ordinal data were analyzed using the χ2 test.
There were no significant between-group differences in participants with versus without otolith organ involvement in terms of their baseline presentation for demographic factors such as age (P = .52) and time since onset of symptoms (P = .04), and with respect to measures of symptom severity (VSI total scores, P = .77), self-perceived handicap (DHI total scores, P = .86), functional status (HAP AAS scores, P = .24), and measures of balance performance (computerized dynamic posturography composite score, P = .94). The key findings are provided in Table 1.
All participants completed the 8-week program of VR. Compliance with the HEP (as measured using the Compliance Rating Scale) was excellent for all participants, and there were no significant between-group differences in this regard (P = .37). More than 80% of the participants performed the exercises at least twice on most days (total compliance rating scores of 1 or 2), with >30% of participants completing the HEP 3 times every day as requested.
Comparative Effectiveness of VR Between Participants with Versus Without Otolith Dysfunction
Few significant differences were identified between the subject groups with respect to change after the program of VR. The key findings are presented below.
Subjective Reports of Improvement
There were no significant differences between participants with versus those without otolith organ involvement with respect to subjective reports of improvement (measured using the Symptom Outcome Score) after the program of VR (P = .65). The majority of participants (94%) reported mild to marked improvement in symptoms after VR, and 1 individual had no symptoms at all remaining at the end of the program. In addition, no participants reported feeling worse after VR, although 2 individuals (5% of the full sample) felt that there had been no change in their symptoms with the exercise program.
Change in Questionnaire Scores and Balance Tests
Significant improvements were identified in most balance and mobility measures and questionnaires after the program of VR for all participants. No significant differences in rehabilitation outcomes were identified in comparisons of participants with versus without otolith organ involvement with respect to mean change from baseline to reassessment in VSI total scores (P = .81), DHI total scores (P = .92), HAP AAS scores (P = .93), DRS scores (P = .54), and measures of balance performance (Table 2). For participants who were currently employed, subjective reports of improvements in the workplace were described by almost 50% of those who identified work-related issues at baseline, and there were no significant differences between the groups in this regard (P = .70; Table 2). For participants who identified significant driving-related problems at baseline, subjective improvements in driving were reported by >80% of participants with additional otolith organ involvement, but by only 13% of those with a purely canal lesion. This difference between the groups was significant (P = .001; Table 2).
The results of this study demonstrated that a relatively low-cost, customized program of VR was effective across a number of key domains, in treating individuals with vestibular dysfunction that was chronic in nature. The successful nature of VR has been identified previously,1 however, many of the variables influencing successful outcome are yet to be studied. By using tests of otolith function, this study was the first to specifically investigate the clinical significance of otolith dysfunction in influencing outcomes after a customized program of VR.
Comparative Effectiveness of Vestibular Rehabilitation
This study determined that there were few significant differences in the response to VR between individuals with versus without otolith organ involvement. No other studies have previously compared these 2 groups, although it has been suggested that a peripheral vestibular disorder with additional involvement of otolith structures is a more severe and extensive lesion and therefore has a poorer prognosis for recovery.5,6 The results of this study do not support this hypothesis. A positive response to VR was identified both for individuals with and individuals without otolith organ involvement, with significant improvements identified in subjective reports of symptom severity, self-perceived handicap, and balance performance. In fact, individuals with additional otolith organ involvement were found to have significantly fewer problems with driving after VR compared to those with a purely canal involvement. This was an unexpected finding considering that driving frequently involves linear acceleration and deceleration motion, and off-axis rotations, which may be problematic for individuals with otolith dysfunction. However, given the documented role of the otolith structures in the maintenance of balance,31,32 it is perhaps more likely that people with otolith organ involvement would experience poorer recovery of balance strategies in standing and walking. Again, this was not the case for the majority of balance and mobility tests used to measure outcome in this study. This finding is in agreement with the study by Basta et al33 who also demonstrated balance and mobility improvements after therapy with and without auditory feedback in individuals with diagnosed otolith dysfunction.27
These outcomes are encouraging and suggest that our current rehabilitation protocols can successfully manage otolith dysfunction. To date, however, no studies have investigated whether exercises that specifically target the otolith structures can improve outcomes for individuals with peripheral vestibular dysfunction. Our clinic in Melbourne, Australia, is currently undertaking a randomized controlled trial to investigate these issues, and outcomes will provide future guidance regarding the optimal components of a customized VR program for this important clinical group.
The results obtained in this study were dependent on the appropriate allocation of participants to the 2 study groups. The sensitivity with which otolith function tests can identify otolith involvement has been reported to range from 40% to 60%,5 and therefore participants with otolith dysfunction may have been misclassified and incorrectly allocated to the group with canal involvement only. Since the completion of this study, the ocular vestibular-evoked myogenic potential test has been developed34 and is considered to provide additional information regarding utricular function. Because new tests of vestibular function are being developed, it will be possible to more comprehensively investigate the clinical significance of otolith dysfunction.
Few significant differences were found in the response to VR of individuals with a diagnosed vestibular disorder that did versus that did not involve the otolith organs of the inner ear. Successful outcomes were identified for the full sample across a number of key domains, with significant improvements identified in subjective reports of symptom severity, self-perceived handicap, and balance performance. More research is required to identify whether specific exercises targeting the otolith structures of the inner ear can improve outcomes in individuals with peripheral vestibular dysfunction.
The authors thank the staff in the audiology departments at the Alfred and the Royal Victorian Eye and Ear Hospitals and Belinda Reid from Cedar Court Rehabilitation Hospital who acted as the reviewing physiotherapist.
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