Quantitative Head Impulse Test Research Articles

Quantitative Oculomotor Assessment in Hereditary Ataxia: Discriminatory Power, Correlation with Severity Measures, and Recommended Parameters for Specific Genotypes

Characterizing bedside oculomotor deficits is a critical factor in defining the clinical presentation of hereditary ataxias. Quantitative assessments are increasingly available and have significant advantages, including comparability over time, reduced examiner dependency, and sensitivity to subtle changes. To delineate the potential of quantitative oculomotor assessments as digital-motor outcome measures for clinical trials in ataxia, we searched MEDLINE for articles reporting on quantitative eye movement recordings in genetically confirmed or suspected hereditary ataxias, asking which paradigms are most promising for capturing disease progression and treatment response. Eighty-nine manuscripts identified reported on 1541 patients, including spinocerebellar ataxias (SCA2, n = 421), SCA3 (n = 268), SCA6 (n = 117), other SCAs (n = 97), Friedreich ataxia (FRDA, n = 178), Niemann-Pick disease type C (NPC, n = 57), and ataxia-telangiectasia (n = 85) as largest cohorts. Whereas most studies reported discriminatory power of oculomotor assessments in diagnostics, few explored their value for monitoring genotype-specific disease progression (n = 2; SCA2) or treatment response (n = 8; SCA2, FRDA, NPC, ataxia-telangiectasia, episodic-ataxia 4). Oculomotor parameters correlated with disease severity measures including clinical scores (n = 18 studies (SARA: n = 9)), chronological measures (e.g., age, disease duration, time-to-symptom onset; n = 17), genetic stratification (n = 9), and imaging measures of atrophy (n = 5). Recurrent correlations across many ataxias (SCA2/3/17, FRDA, NPC) suggest saccadic eye movements as potentially generic quantitative oculomotor outcome. Recommendation of other paradigms was limited by the scarcity of cross-validating correlations, except saccadic intrusions (FRDA), pursuit eye movements (SCA17), and quantitative head-impulse testing (SCA3/6). This work aids in understanding the current knowledge of quantitative oculomotor parameters in hereditary ataxias, and identifies gaps for validation as potential trial outcome measures in specific ataxia genotypes.

Reader response: Teaching Video NeuroImages: Vestibulo-ocular reflex defect in cerebellar stroke.

We read with interest the Teaching Video NeuroImage article by Witsch et al.1 The authors stated that abnormal vestibulo-ocular reflex, which cannot be measured by the naked eye, is indirectly implied by way of observing a corrective catch-up saccade. Our group demonstrated with quantitative head impulse test that catch-up saccade can be generated in acute cerebellar stroke, even when the gain of the vestibulo-ocular reflex is not abnormal.2 We suggest, with the widespread availability of portable video head impulse test,3 that abnormal clinical head impulse test should be rapidly confirmed at point of care by measuring both the vestibulo-ocular reflex gain and catch-up saccade parameters.

Editors' note: Teaching Video NeuroImages: Vestibulo-ocular reflex defect in cerebellar stroke

In “Teaching Video NeuroImages: Vestibulo-ocular reflex defect in cerebellar stroke,” Witsch et al. described a patient with an abnormal vestibulo-ocular reflex with corrective saccade on right head impulse test (HIT) found to have a left flocculonodular cerebellar stroke. They commented that an abnormal HIT is generally associated with peripheral pathology, but that their patient demonstrated that this test has “limited specificity.” On review of this patient's MRI, Lee et al. commented that the lesion is, in fact, posterolateral to the flocculonodular lobe and could not easily explain an abnormal vestibulo-ocular reflex. Tarnutzer et al. agree and note that the lesion is in the region of the cerebellar hemisphere fed by the superior cerebellar artery. Furthermore, they add that the HIT test's specificity is 85%–90%, which is not “limited.” In addition, Chen et al. note that they demonstrated that quantitative HIT can produce a corrective saccade in the setting of cerebellar stroke, even with a normal vestibulo-ocular reflex. Witsch et al. respond that: (1) Their interpretation of the MRI was that the stroke was in the inferior and middle cerebellum (the flocculonodular region), not the flocculonodular lobe; (2) Occam's razor suggests that this lesion must be the explanation for the abnormal vestibulo-occular reflex; (3) It may have been more accurate to say that their finding “refutes the common perception of absolute specificity” of the HIT, rather than saying that HIT has “limited specificity;” and (4) The portable video HIT could be helpful in identifying those patients who have cerebellar infarcts with normal vestibulo-ocular reflex gain but catch-up saccades. In “Teaching Video NeuroImages: Vestibulo-ocular reflex defect in cerebellar stroke,” Witsch et al. described a patient with an abnormal vestibulo-ocular reflex with corrective saccade on right head impulse test (HIT) found to have a left flocculonodular cerebellar stroke. They commented that an abnormal HIT is generally associated with peripheral pathology, but that their patient demonstrated that this test has “limited specificity.” On review of this patient's MRI, Lee et al. commented that the lesion is, in fact, posterolateral to the flocculonodular lobe and could not easily explain an abnormal vestibulo-ocular reflex.

Vestibular Dysfunction in Wernicke's Encephalopathy: Predominant Impairment of the Horizontal Semicircular Canals.

Wernicke's encephalopathy (WE), a metabolic disorder due to thiamine deficiency, manifests with various neurological symptoms and signs. It has been known as a cause of vestibular dysfunction. Preliminary reports have proposed predominant involvement of the horizontal semicircular canals (HSCs). To better characterize the pattern of vestibular impairment in patients with WE using quantitative video head-impulse testing and to review the literature regarding this topic. From January 2014 to December 2016, we retrospectively enrolled five cases of WE that received quantitative video-head-impulse testing (vHIT). We retrieved the clinical features from the medical records and reviewed quantitative head-impulse testing (qHIT) and caloric irrigation. Based on the gain and the number of corrective saccades, the function (normal vs. impaired) of each semicircular canal was rated. In addition, we conducted a MEDLINE and EMBASE search to identify other published cases of WE that had received qHIT. Neuro-otologic and neuro-ophthalmologic findings and vestibular testing results were extracted. A total of 17 patients (own series = 5; published cases = 12) aged 54.6 ± 11 years were included. Key neurologic findings were ataxia of stance and gait (13/13, 100%), spontaneous nystagmus (7/14, 50%), gaze-evoked nystagmus (GEN) (17/17, 100%), positive bedside head-impulse testing for the horizontal canals (16/17, 94%), and memory impairment and mental changes (6/11, 54.5%). Regarding vestibular testing, qHIT (either video based or search-coil based) documented selective bilateral horizontal canal dysfunction with normal or minimal vertical canal impairment (14/14, 100%). On caloric irrigation, bilateral horizontal canal paresis was noted in most cases (10/11, 91%). In WE, signs of both peripheral and central vestibular dysfunction (i.e., GEN, ataxia of stance and gait, abnormal head-impulse testing) were common. Selective or predominant impairment of the HSCs seems to be the most common finding of WE likely related to enhanced vulnerability of the medial vestibular nuclei neurons to thiamine deficiency. Quantitative vHIT of all six semicircular canals is therefore a useful tool for the diagnosis and should be applied in all patients with suspected WE.

Recent advances in head impulse test findings in central vestibular disorders.

The head impulse test (HIT) is used to evaluate the vestibulo-ocular reflex (VOR) during a high-velocity head rotation. Corrective catch-up saccades that occur during or after the HITs usually indicate peripheral vestibular hypofunction, whereas in acute vestibular syndrome, normal clinical (bedside) HITs should prompt a search for a central lesion. However, recent quantitative studies that evaluated HITs using magnetic search coils or video-based techniques have demonstrated that specific patterns of HIT abnormalities are associated with central vestibular disorders. While normal clinical HITs are typical of central lesions, discrepancies have been observed between clinical and quantitative HITs. The horizontal head impulse VOR gains can be significantly reduced unilaterally or bilaterally (positive HITs) in lesions involving the vestibular nucleus, nucleus prepositus hypoglossi, or flocculus. In diffuse cerebellar lesions, the VOR gain during horizontal head impulses may increase (hyperactive) with corrective saccades directed the opposite way. The presence of cross-coupled vertical corrective saccades during horizontal HITs is also suggestive of diffuse cerebellar lesions. Lesions involving the vestibular nucleus, medial longitudinal fasciculus, and cerebellum may show decreased or increased gains of the VOR during vertical HITs. Defining the differences in patterns observed during abnormal HITs may help practitioners localize the responsible lesions in both central and peripheral vestibulopathy.

Bilateral Vestibular Hypofunction in Quantitative Head Impulse Test: Clinical Characteristics in 23 Patients.

To explore clinical features of patients with bilateral vestibular hypofunction (BVH) verified in motorized head impulse test (MHIT). We examined clinical records of 23 adult patients (10 males and 13 females), whose gain of the vestibulo-ocular reflex in the MHIT was bilaterally lowered. Fifteen of 62 unilateral cochlear implant (CI) recipients routinely tested both pre- and postoperatively with the MHIT had BVH. Eight of 198 vestibular outpatients selected to the MHIT due to clinical causes had BVH. Clinical characteristics and a questionnaire regarding current sensations were analyzed. The mean gain±SD in the MHIT was 0.26±0.17 on the right and 0.26±0.14 on the left side. The mean gain in the CI recipients did not differ from that of vestibular outpatients (p>0.05). All outpatients with BVH suffered from oscillopsia, whereas only 46% of CI recipients experienced oscillopsia (p=0.048). Instability was more prominent (p=0.004) and quality of life further decreased (p=0.012) among vestibular outpatients compared with CI patients. Most common etiology for the BVH was meningitis. Other causes were either sudden or progressive loss of labyrinthine function, bilateral Meniére's disease, and ototoxicity. BVH is rare even in a specialized clinic. Vestibular outpatients were more disabled than CI recipients with the BVH.

Evaluation of Quantitative Head Impulse Testing Using Search Coils Versus Video-oculography in Older Individuals

To evaluate the validity of 2D video-oculography (VOG) compared with scleral search coils for horizontal AVOR gain estimation in older individuals. Cross-sectional validation study. Tertiary care academic medical center. Six individuals age 70 and older. Simultaneous eye movement recording with scleral search coil (over right eye) and EyeSeeCam VOG camera (over left eye) during horizontal head impulses. Best estimate search coil and VOG horizontal AVOR gain, presence of compensatory saccades using both eye movement recording techniques. We observed a significant correlation between search coil and VOG best estimate horizontal AVOR gain (r = 0.86, p = 0.0002). We evaluated individual head impulses and found that the shapes of the head movement and eye movement traces from the coil and VOG systems were similar. Specific features of eye movements seen in older individuals, including overt and covert corrective saccades and anticompensatory eye movements, were captured by both the search coil and VOG systems. These data suggest that VOG is a reasonable proxy for search coil eye movement recording in older subjects to estimate VOR gain and the approximate timing of corrective eye movements. VOG offers advantages over the conventional search coil method; it is portable and easy to use, allowing for quantitative VOR estimation in diverse settings such as a routine office-based practice, at the bedside, and potentially in larger scale population analyses.

Vestibular impairment in patients with Charcot-Marie-Tooth disease

This case-control study aimed to determine whether the imbalance in Charcot-Marie-tooth (CMT) disease is caused only by reduced proprioceptive input or whether the involvement of the vestibular nerve is an additional factor. Fifteen patients with CMT disease (aged 48 ± 17 years; 8 women) underwent cervical vestibular-evoked myogenic potentials, which reflect otolith-spinal reflex function, and quantitative horizontal search-coil head-impulse testing, which assesses the high-acceleration vestibulo-ocular reflex of the semicircular canals. Relative to healthy age-matched control subjects, cervical vestibular-evoked myogenic potentials were found to be impaired in 75% of patients (average p13 latency: 23.0 ± 2.7 milliseconds, p = 0.01; average n23 latency: 29.0 ± 1.8 milliseconds, p = 0.01) and the quantitative head-impulse test in 60% of patients (average gain ± 1 SD: 0.67 ± 0.24, p < 0.001). All patients with head-impulse test impairment also showed cervical vestibular-evoked myogenic potential abnormalities, while the reverse was not true. We conclude that the neuropathic process in patients with CMT disease frequently involves the vestibular nerve and that cervical vestibular-evoked myogenic potentials may be more sensitive than quantitative head-impulse testing for detecting vestibular involvement, in particular at an early disease stage.

Head impulse test in unilateral vestibular loss

Quantitative head impulse test (HIT) measures the gain of the angular vestibulo-ocular reflex (VOR) during head rotation as the ratio of eye to head acceleration. Bedside HIT identifies subsequent catch-up saccades after the head rotation as indirect signs of VOR deficit. To determine the VOR deficit and catch-up saccade characteristics in unilateral vestibular disease in response to HIT of varying accelerations. Eye and head rotations were measured with search coils during manually applied horizontal HITs of varying accelerations in patients after vestibular neuritis (VN, n = 13) and unilateral vestibular deafferentation (UVD, n = 15) compared to normal subjects (n = 12). Normal VOR gain was close to unity and symmetric over the entire head-acceleration range. Patients with VN and UVD showed VOR gain asymmetry, with larger ipsilesional than contralesional deficits. As accelerations increased from 750 to 6,000 degrees /sec(2), ipsilesional gains decreased from 0.59 to 0.29 in VN and from 0.47 to 0.13 in UVD producing increasing asymmetry. Initial catch-up saccades can occur during or after head rotation. Covert saccades during head rotation are most likely imperceptible, while overt saccades after head rotation are detectable by clinicians. With increasing acceleration, the amplitude of overt saccades in patients became larger; however, initial covert saccades also became increasingly common, occurring in up to about 70% of trials. Head impulse test (HIT) with high acceleration reveals vestibulo-ocular reflex deficits better and elicits larger overt catch-up saccades in unilateral vestibular patients. Covert saccades during head rotation, however, occur more frequently with higher acceleration and may be missed by clinicians. To avoid false-negative results, bedside HIT should be repeated to improve chances of detection.

Accuracy of the bedside head impulse test in detecting vestibular hypofunction

Objective:To determine the accuracy of the bedside head impulse test (bHIT) by direct comparison with results from the quantitative head impulse test (qHIT) in the same subjects, and to investigate...