Subjective and objective responses to caloric stimulation help separate vestibular migraine from other vestibular disorders.

BACKGROUND: Nystagmus generated during bithermal caloric test assesses the horizontal vestibulo-ocular-reflex. Any induced symptoms are considered unwanted side effects rather than diagnostic information. AIM: We hypothesized that nystagmus slow-phase-velocity (SPV) and subjective symptoms during caloric testing would be higher in vestibular migraine (VM) patients compared with peripheral disorders such as Meniere's disease (MD) and non-vestibular dizziness (NVD). METHODS: Consecutive patients (n = 1373, 60% female) referred for caloric testing were recruited. During caloric irrigations, patients scored their subjective sensations. We assessed objective-measures, subjective vertigo (SVS), subjective nausea (SNS), and test completion status. RESULTS: Nystagmus SPV for VM, MD (unaffected side), and NVD were 29 ± 12.8, 30 ± 15.4, and 28 ± 14.2 for warm irrigation and 24 ± 8.9, 22 ± 10.0, and 25 ± 12.8 for cold-irrigation. The mean SVS were 2.5 ± 1.1, 1.5 ± 1.33, and 1.5 ± 1.42 for warm irrigation and 2.2 ± 1.1, 1.1 ± 1.19, and 1.1 ± 1.16 for cold-irrigation. Age was significantly correlated with SVS and SNS, (p < 0.001) for both. The SVS and SNS were significantly higher in VM compared with non-VM groups (p < 0.001), and there was no difference in nystagmus SPV. VM patients SVS was significantly different to the SVS of migraineurs in the other diagnostic groups (p < 0.001). Testing was incomplete for 34.4% of VM and 3.2% of MD patients. To separate VM from MD, we computed a composite value representing the caloric data, with 83% sensitivity and 71% specificity. Application of machine learning to these metrics plus patient demographics yielded better separation (96% sensitivity and 85% specificity). CONCLUSION: Perceptual differences between VM and non-VM patients during caloric stimulation indicate that subjective ratings during caloric testing are meaningful measures. Combining objective and subjective measures could provide optimal separation of VM from MD.

Capturing nystagmus in the emergency room: posterior circulation stroke versus acute vestibular neuritis.

OBJECTIVES: To compare acute nystagmus characteristics of posterior circulation stroke (PCS) and acute vestibular neuritis (AVN) in the emergency room (ER) within 24 h of presentation. METHODS: ER-based video-nystagmography (VNG) was conducted, recording ictal nystagmus in 101 patients with PCS (on imaging) and 104 patients with AVN, diagnosed on accepted clinical and vestibular test criteria. RESULTS: Patients with stroke in the brainstem (38/101, affecting midbrain (n = 7), pons (n = 19), and medulla (n = 12)), cerebellum (31/101), both (15/101) or other locations (17/101) were recruited. Common PCS territories included posterior-inferior-cerebellar-artery (41/101), pontine perforators (18/101), multiple-territories (17/101) and anterior-inferior-cerebellar-artery (7/101). In PCS, 44/101 patients had no spontaneous nystagmus. Remaining PCS patients had primary position horizontal (44/101), vertical (8/101) and torsional (5/101) nystagmus. Horizontal nystagmus was 50% ipsiversive and 50% contraversive in lateralised PCS. Most PCS patients with horizontal nystagmus (28/44) had unidirectional "peripheral-appearing" nystagmus. 32/101 of PCS patients had gaze-evoked nystagmus. AVN affected the superior, inferior or both divisions of the vestibular nerve in 55/104, 4/104 and 45/104. Most (102/104) had primary position horizontal nystagmus; none had gaze-evoked nystagmus. Two inferior VN patients had contraversive torsional-downbeat nystagmus. Horizontal nystagmus with SPV ≥ 5.8 °/s separated AVN from PCS with sensitivity and specificity of 91.2% and 83.0%. Absent nystagmus, gaze-evoked nystagmus, and vertical-torsional nystagmus were highly specific for PCS (100%, 100% and 98.1%). CONCLUSION: Nystagmus is often absent in PCS and always present in AVN. Unidirectional 'peripheral-appearing' horizontal nystagmus can be seen in PCS. ER-based VNG nystagmus assessment could provide useful diagnostic information when separating PCS from AVN.

Dissociation of caloric and head impulse tests: a marker of Meniere's disease.

A retrospective analysis of the horizontal video head impulse test (vHIT) results and caloric testing results was undertaken on 644 patients who attended a neuro-otology outpatient facility. Presenting symptoms included spontaneous vertigo, positional vertigo, imbalance or chronic subjective dizziness. For 570 patients, the results of vHIT and caloric testing were concordant. Both tests were normal in 500 subjects with an average vHIT gain = 0.92 ± 0.09 (L); 0.98 ± 0.10 (R) and canal paresis (CP) = 7.88 ± 6.12; (range 0-28%). 54 had concordant asymmetries, average ipsilesional vHIT gain = 0.56 ± 0.15, average contralesional vHIT gain = 0.88 ± 0.12. CP = 68.02 ± 24.38 (range 31-100%). 16 subjects had bilateral vestibular hypofunction with average vHIT gains of 0.42 ± 0.20 (L); 0.41 ± 0.19 (R), peak slow phase velocity (SPV) on warm caloric testing = 2.68 ± 2.08, range 0-6°/s (L) and 3.75 ± 3.43 range, 0-10°/s (R). 36 patients showed a dissociation of results between the two tests. In these subjects, the vHIT gain was normal (0.93 ± 0.06 left and 0.98 ± 0.07 right) and the caloric test showed a CP > 30% (48 ± 13.8%). Their final diagnoses included clinically definite Meniere's disease (MD) (n = 27), vestibular schwannoma (VS) (n = 2) vestibular migraine (VM) (n = 1), vestibular neuritis (VN) (n = 5) and unknown (n = 1). No patient with abnormal HSCC gain on vHIT had a normal caloric result. The caloric test complements the vHIT in the assessment of vestibular disorders and is most useful in suspected endolymphatic hydrops. Asymmetric caloric function in the presence of normal horizontal head impulse tests is most commonly associated with Meniere's disease and may function as a diagnostic marker.

Benign positional vertigo, its diagnosis, treatment and mimics.

The diagnosis of benign positional vertigo (BPV) relies on a history of episodic positional vertigo and a distinctive pattern of nystagmus during provocative positional testing. The direction of the induced nystagmus is specific to the affected canal and the velocity profile reflects the underlying mechanism of canalithiasis (free-floating otoconia within the canal duct) or cupulolithiasis (otoconia adherent to the cupula). We review current theories on the pathophysiology of BPV, the clinical history and examination underlying its diagnosis, and recommended repositioning manoeuvres for each of the BPV subtypes. Disorders other than BPV which may present with a similar history and/or positional nystagmus are discussed.

Vestibular-evoked myogenic potentials.

The vestibular-evoked myogenic potential (VEMP) is a short-latency potential evoked through activation of vestibular receptors using sound or vibration. It is generated by modulated electromyographic signals either from the sternocleidomastoid muscle for the cervical VEMP (cVEMP) or the inferior oblique muscle for the ocular VEMP (oVEMP). These reflexes appear to originate from the otolith organs and thus complement existing methods of vestibular assessment, which are mainly based upon canal function. This review considers the basis, methodology, and current applications of the cVEMP and oVEMP in the assessment and diagnosis of vestibular disorders, both peripheral and central.

Tuning characteristics of ocular and cervical vestibular evoked myogenic potentials in intact and dehiscent ears.

Cervical and ocular vestibular evoked myogenic potentials (cVEMPs and oVEMPs) to air-conducted tone bursts (250-2000 Hz) were recorded in 14 patients with superior canal dehiscence (SCD) and 32 healthy controls. For cVEMPs, the most common 'optimal frequency' in control ears (48.2%) was 500 Hz; for oVEMPs, it was 1000 Hz (51.8%). We found a significant interaction between age and frequency, with a shift towards higher-frequency tuning in older subjects. cVEMP and oVEMP tuning in SCD was characterised by a broadening of amplitude and threshold tuning curves. The tendency of cVEMPs to tune to lower frequencies compared to oVEMP was enhanced in SCD. Differences in cVEMP and oVEMP 'optimal frequencies', demonstrated in 57.1% intact ears and 81.3% dehiscent ears, imply differences in the recruitment of hair cells generating these two reflexes. Age-matched oVEMP amplitudes provided excellent separation between SCD and control ears. Although cVEMP amplitudes overlapped between SCD and control ears, better separation was achieved by using a 2-kHz stimulus.

Vestibular evoked myogenic potentials: past, present and future.

Since the first description of sound-evoked short-latency myogenic reflexes recorded from neck muscles, vestibular evoked myogenic potentials (VEMPs) have become an important part of the neuro-otological test battery. VEMPs provide a means of assessing otolith function: stimulation of the vestibular system with air-conducted sound activates predominantly saccular afferents, while bone-conducted vibration activates a combination of saccular and utricular afferents. The conventional method for recording the VEMP involves measuring electromyographic (EMG) activity from surface electrodes placed over the tonically-activated sternocleidomastoid (SCM) muscles. The "cervical VEMP" (cVEMP) is thus a manifestation of the vestibulo-collic reflex. However, recent research has shown that VEMPs can also be recorded from the extraocular muscles using surface electrodes placed near the eyes. These "ocular VEMPs" (oVEMPs) are a manifestation of the vestibulo-ocular reflex. Here we describe the historical development and neurophysiological properties of the cVEMP and oVEMP and provide recommendations for recording both reflexes. While the cVEMP has documented diagnostic utility in many disorders affecting vestibular function, relatively little is known as yet about the clinical value of the oVEMP. We therefore outline the known cVEMP and oVEMP characteristics in common central and peripheral disorders encountered in neuro-otology clinics.

The n10 component of the ocular vestibular-evoked myogenic potential (oVEMP) is distinct from the R1 component of the blink reflex.

OBJECTIVE: Bone-conducted vibration (BCV) in the midline at the hairline (Fz), results in short latency potentials recorded by surface electrodes beneath the eyes - the ocular vestibular-evoked myogenic potential (oVEMP). The early negative component of the oVEMP, n10, is due to vestibular stimulation, however it is similar to the early R1 component of the blink reflex. Here we seek to dissociate n10 from R1. METHODS: Surface potentials were recorded from the infraorbital electromyogram of 10 healthy subjects, 6 patients with bilateral vestibular loss, 2 with unilateral vestibular loss, 4 with facial palsy and 3 with facial and vestibular nerve lesions on the same side. BCV was delivered at Fz, the inion, the glabella or the supraorbital ridge using a tendon hammer or a bone-conduction vibrator. RESULTS: Onset latencies of the n10 evoked by taps at Fz or inion were significantly shorter than the R1 components of blink responses to supraorbital and glabellar stimuli. Upward gaze increased the amplitude of n10 but not R1. The n10 was absent bilaterally in patients with bilateral vestibular loss and beneath the contralesional eye in patients with unilateral vestibular loss, but in both these groups of patients R1 was preserved. In severe facial palsy the R1 component was absent or delayed and attenuated ipsilesionally, but n10 was preserved bilaterally. In subjects with unilateral facial and vestibular nerve lesions (Herpes Zoster of the facial and vestibulocochlear nerves) the dissociation was complete - the ipsilesional R1 was absent or attenuated whereas the ipsilesional n10 was preserved. CONCLUSIONS: n10 is distinguished from R1 by its earlier onset, laterality, modulation by gaze position and dissociation in patient groups. SIGNIFICANCE: The n10 component evoked by BCV at Fz is not the R1 component of the blink reflex.

EMG responses evoked by the termination of galvanic (DC) vestibular stimulation: 'off-responses'.

OBJECTIVE: Vestibular responses in soleus electromyography (EMG) evoked by the sudden onset of galvanic (DC) stimulation ('on-responses') have been described in detail previously. The aim of the present study was to describe responses in soleus triggered by the termination of galvanic stimulation ('off-responses'). METHODS: In 10 healthy human subjects, we studied responses to transmastoid (bilateral) stimuli of 200 ms and 2 s average duration and 3 or 4 mA intensity. We obtained both on- and off-responses using the same raw data. EMG activity was recorded onto tape while current pulses of systematically varying duration were delivered. Averaged on-responses were obtained by triggering from the beginning of the current pulses. Averaged off-responses were obtained by triggering from the termination of the current pulses. RESULTS: Short-latency (SL) and medium latency (ML) off-responses were both obtained in all but one study. The SL and the ML components of the off-responses were present and had similar latencies and amplitudes, but opposite excitability, to the on-responses obtained with the same stimuli. CONCLUSIONS: Off-responses to galvanic vestibular stimulation can be recorded from soleus EMG. Our findings imply that vestibular SL and ML reflex responses in the legs are dependent on the change in the rate of vestibular nerve discharge, not its absolute level. Both on- and off-responses have properties appropriate to a role in maintaining body stability.

Vestibular activation by bone conducted sound.

OBJECTIVE: To examine the properties and potential clinical uses of myogenic potentials to bone conducted sound. METHODS: Myogenic potentials were recorded from normal volunteers, using bone conducted tone bursts of 7 ms duration and 250-2000 Hz frequencies delivered over the mastoid processes by a B 71 clinical bone vibrator. Biphasic positive-negative (p1n1) responses were recorded from both sternocleidomastoid (SCM) muscles using averaged unrectified EMG. The best location for stimulus delivery, optimum stimulus frequency, stimulus thresholds, and the effect of aging on evoked response amplitudes and thresholds were systematically examined. Subjects with specific lesions were studied. Vestibular evoked myogenic potentials (VEMP) to air conducted 0.1 ms clicks, 7 ms/250-2000 Hz tones, and forehead taps were measured for comparison. RESULTS: Bone conducted sound evoked short latency p1n1 responses in both SCM muscles. Ipsilateral responses occurred earlier and were usually larger. Mean (SD) p1 and n1 latencies were 13.6 (1.8) and 22.3 (1.2) ms ipsilaterally and 14.9 (2.1) and 23.7 (2.7) ms contralaterally. Stimuli of 250 Hz delivered over the mastoid process, posterosuperior to the external acoustic meatus, yielded the largest amplitude responses. Like VEMP in response to air conducted clicks and tones, p1n1 responses were absent ipsilaterally in subjects with selective vestibular neurectomy and preserved in those with severe sensorineural hearing loss. However, p1n1 responses were preserved in conductive hearing loss, whereas VEMP to air conducted sound were abolished or attenuated. Bone conducted response thresholds were 97.5 (3.9) dB SPL/30.5 dB HL, significantly lower than thresholds to air conducted clicks (131.7 (4.9) dB SPL/86.7 dB HL) and tones (114.0 (5.3) dB SPL/106 dB HL). CONCLUSIONS: Bone conducted sound evokes p1n1 responses (bone conducted VEMP) which are a useful measure of vestibular function, especially in the presence of conductive hearing loss. For a given perceptual intensity, bone conducted sound activates the vestibular apparatus more effectively than air conducted sound.

Selective effects of ageing on vestibular-dependent lower limb responses following galvanic stimulation.

OBJECTIVES: To examine the influence of ageing on electromyographic (EMG) responses to galvanic vestibular stimulation (GVS) in the lower limbs and to define normal values. METHODS: EMG responses to 4 mA/20 ms transmastoid binaural GVS were recorded from the soleus muscles of 70 healthy adults aged 24-85 years. Short (SL) and medium latency (ML) vestibular-dependent reflex latencies and amplitudes were measured from averaged rectified EMG. Side to side differences were examined in 30 subjects, using monaural stimulation, and expressed as an asymmetry ratio (AR). RESULTS: SL reflexes to transmastoid binaural stimulation were absent in 10 of the 25 subjects over the age of 60. ML responses were present in all subjects. SL reflex amplitudes decreased from 24.4+/-12.4% (mean+/-SD) in the 3rd decade to 7.6+/-6.2% in the 8th and 9th decades. The ML reflex amplitudes showed a tendency to increase with age. The mean AR for SL reflex amplitudes increased from 12.1% in the 3rd decade to 80.7% in the 8th and 9th decades but that for ML amplitudes did not change significantly. The average SL and ML response onset latencies were 56.5+/-7.5 and 97.2+/-9.4 ms. SL onset latencies were significantly delayed with age. Both SL and ML responses were highly reproducible between experiments. CONCLUSIONS: SL and ML responses behave differently in response to age. The decrease in SL reflex amplitudes correlates well with previously described age-related morphological changes. Preservation of the ML reflex may reflect central adaptation to reduced afferent input. SL and ML responses are potentially useful measures of vestibular-spinal function, which may have a role in the assessment of older subjects with dysequilibrium. These reflexes need to be interpreted in the context of age.

Characteristics of tone burst-evoked myogenic potentials in the sternocleidomastoid muscles.

HYPOTHESIS: Optimum stimulus parameters for tone burst-evoked myogenic responses can be defined. These optimized responses will be similar to those evoked by clicks in the same subjects. BACKGROUND: Loud tones give rise to myogenic responses in the anterior neck muscles, similar to click-evoked potentials, and are likely to be saccular in origin. METHODS: Tone burst-evoked and click-evoked myogenic potentials were measured from the sternocleidomastoid muscles of 12 normal subjects (6 men, 6 women) during tonic activation. The effects of tone burst frequency and duration were systematically investigated. Thresholds were measured and compared with click thresholds for the same subjects. Patients with specific lesions were studied using both stimuli. RESULTS: Tone burst-evoked responses showed frequency tuning, with the largest reflex amplitudes at either 500 Hz or 1 kHz. As the stimulus duration was increased, using a constant repetition rate, there was an increase in the reflex amplitudes followed by a decline. The overall optimum stimulus duration was 7 milliseconds. The mean tone burst threshold was 114.4-dB sound pressure level. Stimulus thresholds for click-evoked and tone burst-evoked responses were significantly correlated. Tone burst-evoked and click-evoked responses were present after stimulation of the affected ears of subjects with profound sensorineural hearing loss. Four subjects who had previously undergone vestibular neurectomy had an absence of click and tone burst-evoked responses on the side of the lesion, confirming their vestibular dependence. CONCLUSION: Tone burst-evoked myogenic responses are similar to click-evoked responses but require lower absolute stimulus intensities. To be certain of an optimum response, a stimulus duration of 7 milliseconds, an adequate intensity, and frequencies of both 500 Hz and 1 kHz should be used.

Vestibulocollic reflexes: normal values and the effect of age.

OBJECTIVES: To define normal values and examine the influence of ageing on vestibulocollic reflexes (VCR). METHODS: Vestibulocollic responses to 100 dB (normal hearing level; NHL) clicks, forehead taps and galvanic stimulation were measured in 70 healthy adults aged 25-85 years. RESULTS: Click- and galvanic-evoked responses were present bilaterally in all subjects below 60. Average click-evoked response amplitudes decreased with age, with a pronounced decline of 25-30% per decade from the 6th decade. The average click thresholds increased from 85 dB in the third decade to 96.5 dB in the 8th and 9th decades. Average galvanic-evoked VCR amplitudes decreased sharply from the seventh decade. Tap-evoked reflex amplitudes showed a milder decrease. When side to side differences in amplitude were expressed as asymmetry ratios (AR) in subjects below the age of 60, values of up to 35 and 46% were obtained for click amplitudes corrected and uncorrected for background electromyogram (EMG), up to 61% for both corrected and uncorrected tap response amplitudes, and up to 41 and 55% for corrected and uncorrected galvanic-evoked responses. CONCLUSIONS: A normative range of values can be specified for click- and galvanic-evoked VCRs for subjects up to the age of 60. Click- and galvanic-evoked VCR amplitudes decrease rapidly thereafter while tap-evoked responses are less affected. These changes are probably due to morphological changes in the vestibular system occurring with ageing and are more marked than in several previous reports of age-related changes in caloric responses and vestibulo-ocular reflexes.

Vestibulospinal reflexes: quantitative effects of sensory feedback and postural task.

Vestibulospinal and vestibulocollic reflexes evoked by galvanic stimulation were studied in 20 normal volunteers. In an initial "baseline" study, subjects stood unsupported on a flat surface and a narrow base with their eyes shut and with their heads rotated to the left. The effects of vision, external support and increasing stance width were examined both individually and in combination. In a second series, the effects of the same factors were examined while subjects stood on a compliant surface. Short latency (SL) and medium latency (ML) vestibulospinal reflex responses were evoked using 4 mA/20 ms galvanic vestibular stimulation (GVS) and measured from the right soleus muscle. Vestibulocollic reflexes to short duration galvanic stimulation (4 mA/2 ms) were also measured under similar conditions. Both SL and ML vestibulospinal reflexes decreased significantly and to a similar degree with vision, external support and increasing stance width on a flat surface. On the compliant surface, stance width did not result in a decrease in the ML reflex. Reflex amplitudes further decreased in a non-linear fashion with each additional sensory modality ("factor") that was made available; the degree of attenuation due to the addition of a second and third factor closely approximated the product of the effect of each factor in isolation. Standing on a compliant surface resulted in enhancement of average SL and ML reflexes under all conditions. Vestibulocollic reflexes in contrast showed no significant modulation with vision, external support and stance width. The dissociation between vestibulocollic and vestibulospinal reflexes indicates that the modulation of vestibulospinal reflexes with task occurs proximal to the primary vestibular afferents. Vestibulospinal reflexes were largest when subjects stood on a narrow base, on a compliant surface, deprived of vision and external support, consistent with the importance of vestibular function under these conditions. Although attenuated, vestibulospinal reflexes were preserved in most subjects even when vision and external support were available and a wider stance width was adopted. The combination of different factors caused a multiplicative attenuation of the initial response.