The effect of self-management vestibular rehabilitation on persistent postural-perceptual dizziness.

Objective: To investigate the effects of self-management vestibular rehabilitation (VR) on the subjective symptoms of dizziness and postural stability in persistent postural-perceptual dizziness (PPPD). Study design: Retrospective case review. Methods: The medical records of 30 patients newly diagnosed with PPPD based on the Bárány Society's diagnostic criteria were reviewed. Nineteen patients (4 males and 15 females; age range 27-84 years, mean age ± standard deviation 57.4 ± 14.2 years) who was newly instructed to self-management VR were included and instructed to perform self-management VR for 2 months. Results: One patient did not visit the outpatient clinic again, and in the remaining 18 patients, 4 (22%) discontinued VR at their own discretion. In the 12 patients who completed 2 months of VR (67%), there was a significant improvement in Niigata PPPD Questionnaire (NPQ) and Dizziness Handicap Inventory (DHI) scores after VR compared to those before VR (p < .05). However, the mean velocity of center of pressure (COP) movement (velocity) and the envelopment area traced by COP movement (area), as well as the Romberg ratio and foam ratio of velocity and area, did not differ significantly after VR when compared to those before VR (p > .05). Conclusions: For PPPD, self-management VR improved subjective symptoms of dizziness, but not stability of standing posture. It is necessary to improve patients' adherence to the treatment. Level of evidence: 4.

Visual fixation suppression of caloric nystagmus in progressive supranuclear palsy - A comparison with Parkinson's disease.

BACKGROUND: Impairment of visual fixation suppression (VS) in progressive supranuclear palsy (PSP) is not well documented. OBJECTIVE: To evaluate the usefulness of impaired VS of caloric nystagmus as an index for differential diagnosis between PSP and Parkinson's disease (PD), which is often difficult, especially in the early stage. METHODS: Subjects comprised 26 PSP patients and 26 PD patients clinically diagnosed at Tokyo Metropolitan Neurological Hospital. We retrospectively investigated VS of caloric nystagmus, horizontal pursuit, saccades, and horizontal optokinetic nystagmus recorded on direct-current-electronystagmography, and neuroradiological findings. RESULTS: The median of the average VS% was 0% and 50.0% in PSP and PD patients, respectively. In PSP, VS was impaired even in the early stage of disease. We found a significant correlation between VS and velocity of saccades or maximum slow phase velocity of optokinetic nystagmus only in PSP patients. PSP patients with atrophy of the subthalamic nucleus or with decreased blood flow in the frontal lobe showed significantly more severe impairment of VS. CONCLUSIONS: VS may be a useful biomarker to differentiate patients with PSP from those with PD. Cerebellar networks that connect with the cerebral cortex and basal ganglia may contribute to impaired VS of caloric nystagmus in PSP.

Cervical Vestibular Evoked Myogenic Potentials That Are Absent at 500 Hz But Present at 1000 Hz Are Characteristic of Endolymphatic Hydrops-Related Disease.

OBJECTIVES: It remains unclear whether the dominance of 1000 Hz responses over responses at 500 Hz in cervical vestibular evoked myogenic potentials (cVEMPs) are characteristic of endolymphatic hydrops (EH), due to the presence of patients with absent responses at both frequencies. The purpose of the present study is to examine whether the dominant cVEMP responses at 1000 Hz over 500 Hz are characteristic findings of EH-related diseases among patients who show various cVEMP findings. DESIGN: We retrospectively reviewed the medical records of 470 consecutive patients who underwent cVEMP testing with short-tone bursts at both 500 Hz and 1000 Hz. We categorized the cVEMP responses of these 470 patients into the following five groups: (group 1) present responses at both frequencies bilaterally, (group 2) present responses at 500 Hz but absent at 1000 Hz on at least one side, (group 3) absent responses at 500 Hz but present at 1000 Hz on at least one side, (group 4) absent responses at both frequencies on one side and present at both frequencies on the other side, and (group 5) absent responses at both frequencies bilaterally. We compared the proportion of EH-related diseases between each group and the other four groups and then investigated any increased or decreased disease incidence in each group. RESULTS: In group 3, the proportion of EH-related disease was significantly higher (p < 0.01), and the incidence of an EH-related disease was greatly increased (standard residual value > 3). CONCLUSIONS: cVEMPs that are absent at 500 Hz and present at 1000 Hz may be characteristic of EH-related disease.

Minimally important differences for subjective improvement in postural stability in patients with bilateral vestibulopathy.

OBJECTIVE: To determine minimally important differences (MIDs) for subjective improvement in postural stability after a therapeutic intervention in patients with bilateral vestibulopathy (BVP). METHODS: Thirteen BVP patients received noisy galvanic vestibular stimulation (nGVS) for 30 min and their static posture with eyes closed was monitored after the stimuli. The velocity of the center of pressure (COP) movement, the area enclosed by the COP movement, and the root mean square (RMS) of the displacement of the COP were measured for 30 s. Subjective evaluation of postural stability after nGVS was graded as worsened, slightly worsened, unchanged, slightly improved and improved in comparison with postural stability measured without nGVS. Anchor-based methods were used to estimate MIDs for subjective improvement. Velocity, area and RMS for each anchor-response group were averaged (2 sessions, each with 5 measurement periods during 3 h after the stimuli). The mean changes between the slightly improved group and unchanged group were used as estimates for MID for improvement. RESULTS: A total of 129 anchors were analyzed. Subjective evaluations numbered 83 (64%) for unchanged and 33 (26%) for slightly improved. Anchor-based methods yielded estimates for MIDs of -0.43 cm/s in velocity improvement (p < 0.01), -0.77 cm2 for area improvement (p < 0.01) and -0.23 cm for RMS improvement (p < 0.001). CONCLUSION: The present study provides the estimation of MIDs for improving postural stability in BVP patients and may be useful for interpreting whether the results from clinical trials are meaningful in future studies.

Utriculo-ocular pathway dysfunction is more frequent in vestibular migraine than probable vestibular migraine.

BACKGROUND: Abnormal vestibular function has been reported in patients with vestibular migraine (VM). However, it is unclear whether the proportion of patients with vestibular dysfunction differs between the diagnoses of VM and probable VM (PVM). METHODS: We reviewed the medical records of 1736 patients who underwent cervical vestibular-evoked myogenic potential testing to air-conducted sound (ACS cVEMP), ocular VEMP testing to bone-conducted vibration (BCV oVEMP), and caloric testing. We used the diagnostic criteria for VM provided in the appendix of the International Classification of Headache Disorders 3 Beta, and the diagnostic criteria consensus published by the Barany Society and the International Headache Society for PVM. Twenty-two VM patients and a further 22 PVM patients were included. Binomial logistic regression analyses were performed to see whether the subjects' age, sex, or the diagnostic certainty of VM (i.e., VM vs. PVM) have an association with the presence of vestibular dysfunction. RESULTS: There was no significant association between the diagnostic certainty of VM and abnormality in caloric or ACS cVEMP testing. On the other hand, VM had a significant positive association with abnormality in BCV oVEMPs compared with PVM. CONCLUSION: VM is associated with dysfunction of the utriculo-ocular pathway more frequently than PVM, suggesting that the pathophysiology of VM involves the utriculo-ocular pathway.

Acute bilateral vestibulopathy with simultaneous involvement of both superior and inferior vestibular nerves.

We report a case of acute vestibulopathy with the simultaneous involvement of both superior and inferior vestibular nerves on both sides. A 36-year-old female presented with dizziness, oscillopsia and a walking impairment subsequent to a high fever. Vestibular function tests including caloric testing, video head impulse testing (vHIT) and cervical and ocular vestibular evoked myogenic potentials (cVEMPs and oVEMPs) were performed. In the first examination, vHIT and caloric testing showed severe impairments in all three semicircular canals in each ear, and both cVEMPs and oVEMPs were absent on both sides. During a 1-year follow-up, the gain of vHIT gradually recovered by more than 0.5 to normal. cVEMPs also recovered to normal on both sides while oVEMPs remained absent on both sides. This is the first reported case of acute bilateral vestibulopathy with simultaneous involvement of both superior and inferior vestibular nerves on both sides. Repeated evaluation of vestibular function using vHIT, cVEMPs and oVEMPs is helpful to assess the time course of recovery in patients with vestibulopathy.

Aging Is a Risk Factor for Utricular Dysfunction in Idiopathic Benign Paroxysmal Positional Vertigo.

Benign paroxysmal positional vertigo (BPPV) is the most common cause of balance disorders in the elderly. Dislodgement of the otoconia in BPPV might have an association with damage to the otolith organs. The aim of this study was to investigate whether aging is a risk factor for otolith organ dysfunction in idiopathic BPPV. We retrospectively reviewed the medical records of 112 consecutive idiopathic BPPV patients who underwent cervical VEMP testing to air-conducted sound (ACS cVEMP), ocular VEMP testing to bone-conducted vibration (BCV oVEMP), and caloric testing. We performed binomial logistic regression analyses to see whether age, the side affected by BPPV or the canal affected by BPPV have an association with the presence of peripheral vestibular dysfunction in idiopathic BPPV patients. The elderly group (aged ≥65 years) had a significantly positive association with abnormalities in BCV oVEMPs (p = 0.0109), while the side affected by BPPV (p = 0.598) and the canal affected by BPPV (p = 0.576) did not. The odds ratio of the abnormal BCV oVEMPs for the elderly group compared with the non-elderly group (aged < 65 years) was 2.676 (95% confidence interval, 1.254-5.079). The elderly group had no significant association with the abnormalities in ACS cVEMPs (p = 0.0955) or caloric testing (p = 0.488). Dysfunction of the utricle, where the dislodgement of the otoconia mainly occurs, is affected by aging in idiopathic BPPV.

Clinical features of otolith organ-specific vestibular dysfunction.

OBJECTIVE: To elucidate the clinical features and vestibular symptoms of patients with otolith organ dysfunction in the presence of normal function of the semicircular canals. METHODS: We reviewed the clinical records of 277 consecutive new patients with balance disorders who underwent testing of cervical and ocular vestibular evoked myogenic potentials (cVEMPs and oVEMPs) as well as caloric testing and video head impulse testing (vHIT). RESULTS: We identified 76 patients who showed normal caloric responses and normal vHIT findings in each SCC plane, but abnormal responses in cVEMP and/or oVEMP testing. Benign paroxysmal positional vertigo (BPPV) was the most common diagnosis. 37% of patients could not be categorized into any of the established clinical entities that could cause a balance disorder and did not show sensorineural hearing loss. The most common clinical manifestation in the idiopathic cases was recurrent rotatory vertigo with a duration of 1-12 h. CONCLUSIONS: The most common diagnosis of otolith organ-specific vestibular dysfunction was BPPV. The most common clinical manifestation in the idiopathic cases was recurrent rotatory vertigo. SIGNIFICANCE: Specific dysfunction of the otolith organs occurs in association with some of the undiagnosed patients with recurrent rotatory vertigo.

Effects of Peripheral Vestibular Dysfunction on Dynamic Postural Stability Measured by the Functional Reach Test and Timed Up and Go Test.

OBJECTIVE: To investigate the influence of vestibular function on dynamic postural stability assessed by the functional reach test (FRT) and the timed up and go test (TUG). STUDY DESIGN: Retrospective study. SETTING: Tertiary referral center. SUBJECTS AND METHODS: The FRT and TUG were performed in 399 patients with dizziness. The effects of peripheral vestibular dysfunction assessed by the caloric test and cervical vestibular evoked myogenic potentials (cVEMPs) to air-conducted sound (500 Hz, tone burst) on the results of FRT and TUG were analyzed. RESULTS: Neither FRT nor TUG scores showed significant differences in relation to the results of the caloric test ( P > .3). The FRT scores in patients who showed abnormal cVEMP responses on both sides were significantly smaller than those in patients who showed normal cVEMP responses ( P < .01). The TUG scores in patients who showed abnormal cVEMP responses on both sides were significantly greater than those in patients who showed normal cVEMP responses ( P < .05). CONCLUSION: The vestibulo-spinal reflex mediated by the saccule and its afferents is one of the factors that influence the maintenance of dynamic postural stability as measured by FRT and TUG.

Characteristics of vertigo and the affected vestibular nerve systems in idiopathic bilateral vestibulopathy.

CONCLUSION: Vertigo attacks in IBV patients involving both the superior and inferior vestibular nerve systems were significantly more severe than vertigo attacks in patients with selective involvement of the inferior vestibular nerve system alone. OBJECTIVE: To investigate the relationship between the frequency and duration of vertigo and the affected vestibular nerve system in idiopathic bilateral vestibulopathy (IBV). METHODS: This study categorized 44 IBV patients into the following three sub-groups according to the affected vestibular nerve system: superior, inferior, and mixed type. These patients were also categorized into the following three sub-groups according to their clinical time course: progressive type showing no episodes of vertigo, sequential type showing recurrent vertigo attacks and single-attack type showing a single episode of vertigo. RESULTS: Ten, 11 and 23 patients were classified as the superior, the inferior, and the mixed type, respectively. Seventeen, 23, and four patients were classified as the progressive, the sequential, and the single-attack type, respectively. For the patients having one or more vertigo attacks, the duration of the vertigo attack was longer than 24 h in 69% of the mixed type, and the duration of vertigo in the mixed type was significantly longer than that in the inferior type (p < 0.05).

Idiopathic latent vestibulopathy: a clinical entity as a cause of chronic postural instability.

The objective of this study is to describe a new clinical entity of idiopathic latent vestibulopathy (ILV), in which patients have unilateral or bilateral vestibulopathy combined with unsteadiness but without episodic vertigo, auditory disturbance, or a medical history suggesting the presence of vestibulopathy. A retrospective study of 1,233 consecutive new outpatients was conducted. Two-legged stance tasks were performed by 11 patients identified as having ILV in four conditions: eyes open with and without foam rubber, and eyes closed with and without foam rubber. We examined six parameters: the velocity of movement of the center of pressure (COP) with eyes closed/foam rubber, the envelopment area traced by the movement of the COP with eyes closed/foam rubber, Romberg's ratio of velocity and area with foam rubber, and the foam ratios of velocity and area with eyes closed. Multiple regression analyses were performed in order to explore the relationship between the presence of ILV and the six parameters recorded during foam posturography, while adjusting for the subjects' gender and age. The presence of ILV had a significantly positive relationship with the values of 4 of the 6 parameters. Even though six patients showed only unilateral vestibulopathy, their median value in all 6 parameters was greater than that of healthy controls. ILV could be a clinical entity accountable for postural instability.

Involvement of vestibular organs in idiopathic sudden hearing loss with vertigo: an analysis using oVEMP and cVEMP testing.

OBJECTIVE: To investigate the extent of vestibular lesions in idiopathic sudden hearing loss (ISHL) with vertigo. METHOD: We reviewed the clinical records of 25 consecutive new patients with ISHL with vertigo. We classified patients based on their pattern of vestibular dysfunction. All patients showed cochlear damage and were labeled C (cochlear) type. If a patient showed abnormal cervical vestibular evoked myogenic potential (cVEMP), ocular VEMP (oVEMP) or caloric responses, an S (saccule), U (utricule) or L (lateral semicircular canal) respectively was added to their label. RESULTS: All patients underwent cVEMPs and caloric tests. Sixteen (64%) and 13 (52%) showed abnormal cVEMPs and caloric responses, respectively, on the affected side. Among the 23 patients who underwent oVEMPs, 10 (43%) showed abnormal oVEMPs on the affected side. Of these 23 patients, 6 (26%) were classified as C type, 4 (17%) as CS type, 1 (4%) as CL type, 1 (4%) as CSU type, 2 (9%) as CSL type, 1 (4%) as CUL type, 8 (35%) as CSUL type. CONCLUSION: The vestibular end organs close to the cochlea tended to be preferentially affected. SIGNIFICANCE: It is likely that vestibular dysfunction extends from organs close to the cochlea to those further from the cochlea.

Power spectral analysis of postural sway during foam posturography in patients with peripheral vestibular dysfunction.

OBJECTIVE: To assess the frequency-domain characteristics of postural instability caused by peripheral vestibular dysfunction by performing a power spectral analysis of the center of pressure (COP) sway during foam posturography. METHODS: Data were obtained from 78 patients and 163 controls. Two-legged stance tasks were performed in 4 conditions: eyes open with and without foam rubber, and eyes closed with and without foam rubber. We estimated the power spectrum of the acceleration signal using the maximum entropy method. The areas under the curve (AUCs) of power spectral density of the COP were calculated across low-frequency (0.02 to 0.1 Hz, LF-AUC), middle-frequency (0.1 to 1Hz, MF-AUC), and high-frequency (1 to 10 Hz, HF-AUC) ranges. We performed binomial logistic regression analyses to see whether the AUCs of selected bandwidths of COP have a stronger association with the presence of peripheral vestibular dysfunction in comparison with the velocity and area in the eyes closed/foam rubber condition. RESULTS: In both the controls and patients, the MF-AUC was significantly larger than the LF-AUC or HF-AUC in the eyes closed/foam rubber condition. In this condition, the presence of peripheral vestibular dysfunction had a significantly positive relationship with MF-AUC and HF-AUC (p < 0.05) and the MF-AUC of the anterior-posterior axis showed a stronger association with the presence of peripheral vestibular dysfunction than area. CONCLUSION: An increase in activity at middle frequency movements could be characteristic of peripheral vestibular dysfunction when standing on foam rubber with the eyes closed.

Postural stability in vestibular neuritis: age, disease duration, and residual vestibular function.

OBJECTIVES/HYPOTHESIS: To assess the influence of factors that can affect postural instability in vestibular neuritis (VN). STUDY DESIGN: Retrospective data collection study. METHODS: Foam posturography was performed in 58 VN patients. We examined six variables: the velocity of movement of the center of pressure and the envelopment area in eyes closed/foam rubber condition, Romberg's ratios of velocity and area with foam rubber, and the foam ratios of velocity and area with eyes closed. Multiple regression analyses were performed to explore the relationship between these variables and the following independent variables: gender, age, canal paresis (CP) percentage, and disease duration. RESULTS: All six variables were positively associated with age, CP percentage, and a disease duration of 10 days or less (P < .05) except for Romberg's ratio of velocity with foam rubber, which was positively associated with CP percentage and a disease duration of 10 days or less (P < .05), but not with age (P > .05). CONCLUSIONS: VN patients show poor postural performance, which is affected by age, residual vestibular function, and disease duration. Once a VN patient passes the acute phase of the vertigo attack, it is likely that age and residual vestibular function make a greater contribution to postural control. LEVEL OF EVIDENCE: 3b.

Factors affecting postural instability in Meniere's disease.

OBJECTIVE: To assess the influence of factors that can affect the postural instability of Ménière's disease (MD) patients. STUDY DESIGN: Case-control study. SETTING: Outpatient clinic in a university hospital. SUBJECTS AND METHODS: Fifty-four definite MD patients and 66 controls were included. Two-legged stance tasks were performed in 4 conditions: eyes open with and without foam rubber and eyes closed with and without foam rubber. We examined 6 variables: the velocity of movement of the center of pressure (COP), the envelopment area traced by the movement of the COP, Romberg's ratio of velocity and area, and the foam ratios of velocity and area. For patients, stepwise multiple regression analyses were performed to explore the relationship between the 6 variables and the following independent variables: gender, age, the presence of abnormal caloric and/or cervical vestibular evoked myogenic potential (cVEMP) responses, the time elapsed since the last vertigo attack, and the disease duration. RESULTS: The presence of MD had a significantly positive relationship with all 6 of the variables (P < .05). The presence of abnormal caloric and/or cVEMP responses had a significantly positive relationship with Romberg's ratio of velocity (P < .05) and area (P < .01). The shorter time interval from last vertigo attack to measurement had a significantly positive relationship with the foam ratio of area (P < .01). CONCLUSION: MD patients show poor postural performance, which is affected by the existence of their peripheral vestibular function and the shorter time interval from last vertigo attack to measurement.

Diagnostic usefulness of multifrequency tympanometry for Ménière's disease.

Multifrequency tympanometry (MFT) is the measurement of the impedance of the middle ear transmission system at a wide range of frequencies from 200 Hz to 2 kHz. A potential use of MFT as a new diagnostic tool for detecting endolymphatic hydrops has recently been reported. However, its clinical usefulness for diagnosing Ménière's disease (MD) remains unclear. To evaluate the clinical usefulness of MFT as a new qualitative and diagnostic test for MD, we performed MFT in 70 patients with unilateral or bilateral MD and in 29 normal control subjects. The width of double peaks in the admittance tympanograms (Y width) at 2 kHz and the resonance frequency (RF) were analyzed, and receiver operating characteristic (ROC) curves were constructed. The Y width in MD-affected ears was significantly greater than that in control ears (p < 0.001). The RF in MD-affected ears was significantly lower than that in control ears (p < 0.01). Neither the Y width nor RF had a significant relationship with hearing levels or the results of caloric and vestibular myogenic potential testings. The area under the ROC curve was 0.71 for the Y width and 0.66 for the RF. At the optimal cutoff points, the sensitivity and specificity of the Y width were 47.3 and 86.8%, respectively, and those of the RF were 41.3 and 84.2%, respectively. These results indicated that MFT is significantly associated with the presence of MD, but its diagnostic accuracy is only modest. MFT is a simple, noninvasive test, which should be considered as a complementary test in the diagnosis of MD.

Clinical characteristics of inferior vestibular neuritis.

CONCLUSIONS: Inferior vestibular neuritis (IVN) is a relatively minor subtype of vestibular neuritis (VN) and its clinical characteristics are unique. OBJECTIVES: To clarify clinical characteristics of IVN in comparison with conventional VN. METHODS: This was a retrospective case series review. Caloric responses and cervical vestibular evoked myogenic potential (cVEMP) responses were measured in 71 patients with VN. The patients were classified into three groups: (1) IVN group, who showed only asymmetrical cVEMP responses; (2) superior VN (SVN) group, who showed only asymmetrical caloric responses; (3) total VN (TVN) group, who showed asymmetrical responses in both tests. The clinical records of time course of subjective symptoms (duration of attack, duration of hospitalization, and time to remission) were reviewed and other profiles (age, sex, affected side, acute symptoms, and sequelae) were evaluated. RESULTS: Of the 71 patients with VN, 13 (18%) were classified as having IVN. The mean age and time to remission of patients with IVN (44.2 ± 4.8 years, 0.9 ± 0.5 months) were significantly lower and shorter, respectively, than those of patients with TVN (57.3 ± 2.5 years, 4.9 ± 4.7 months). There were no significant differences in other symptoms and profiles among the three groups. No patients with IVN showed benign paroxysmal positional vertigo as a sequela.

Admittance tympanometry with 2-kHz probe tones in patients with low-frequency hearing loss.

OBJECTIVES/HYPOTHESIS: To assess the reliability of admittance tympanometry with 2-kHz probe tones in diagnosing ears with endolymphatic hydrops in patients with low-frequency hearing loss. STUDY DESIGN: Case-control study. METHODS: Thirty-six Japanese patients with low-frequency hearing loss (including 21 with Mènière disease, three with delayed endolymphatic hydrops, and 12 with acute or repetitious low-frequency sensorineural hearing loss), 18 patients with other types of hearing loss, and 16 subjects with normal hearing were enrolled at University of Tokyo Hospital. We measured the width of the splitting peaks in the admittance tymapnometry with 2-kHz probe tones. RESULTS: Widths of the probe pressure corresponding to splitting peaks of admittance (Y) tympanometry were significantly greater in the ears with endolymphatic hydrops than in the ears without endolymphatic hydrops in patients with low-frequency hearing loss. Furthermore, the widths in the ears with endolymphatic hydrops were greater than those in ears with other types of hearing loss. Widths of >255 daPa were observed in 38% of ears with endolymphatic hydrops and low-frequency hearing loss and in 21% of ears with other types of hearing loss. CONCLUSIONS: The current study demonstrated that wide splitting peaks of Y tympanometry are more frequently observed in ears showing low-frequency hearing loss than in those with other types of hearing loss, indicating that Y tympanometry can be used to diagnose endolymphatic hydrops in daily practice.

Bilateral vestibulopathy with dissociated deficits in the superior and inferior vestibular systems.

OBJECTIVES: The aim of this study was to reveal the clinical characteristics of dissociated bilateral vestibulopathy (BV) affecting the superior vestibular nerve system on one side and the inferior vestibular nerve system on the other side. It is probable that BV does not always show bilateral deficits of the same vestibular nerve system. METHODS: In a retrospective study of 2,752 consecutive new patients, 1,560 patients had undergone both caloric testing and cervical vestibular evoked myogenic potential testing. All 1,560 patients had also undergone a battery of tests including standardized neurologic, neuro-otologic, neuro-ophthalmologic, and audiological examinations. RESULTS: Forty-three patients (2.8% of 1,560 patients) were given a diagnosis of dissociated BV. Among them, 10 patients (23%) had Meniere's disease and 6 patients (14%) had vestibular neuritis. Eighteen patients (42%) did not have any identifiable disease involving the peripheral vestibule, and 9 patients (21%) could be regarded as having a novel subtype of idiopathic BV. CONCLUSIONS: Although dissociated BV might be induced by some of the same causes that provoke bilateral vestibular dysfunction, a definite proportion of the patients did not have any identifiable causes of dissociated vestibular dysfunction. Idiopathic cases could be categorized into a novel subtype of idiopathic BV.