Continuous Head Motion is a Greater Motor Control Challenge than Transient Head Motion in Patients with Loss of Vestibular Function.

Background. The vestibular system is vital for gaze stability via the vestibulo-ocular reflex, which generates compensatory eye motion in the direction opposite to head motion. Consequently, individuals with peripheral vestibular loss demonstrate impaired gaze stability that reduces functional capacity and quality of life. To facilitate patients' compensatory strategies, two classes of gaze stabilization exercises are often prescribed: (i) transient (eg, ballistic) and (ii) continuous. However, the relative benefits of these two classes of exercises are not well understood. Objective. To quantify head motion kinematics in patients with vestibular loss while they performed both classes of exercises. Methods. Using inertial measurement units, head movements of 18 vestibular schwannoma patients were measured before and after surgical deafferentation and compared with age-matched controls. Results. We found that the head movement during both classes of exercises paralleled those of natural head movement recorded during daily activities. However, head movement patterns were more informative for continuous than transient exercises in distinguishing patients from healthy controls. Specifically, we observed coupling between kinematic measures in control subjects that was absent in patients for continuous but not transient head motion exercises. In addition, kinematic measures (eg, cycle duration) were predictive of standard clinical measures for continuous but not transient head motion exercises. Conclusions. Our data suggest that performing continuous head motion is a greater motor control challenge than transient head motion in patients with less reliable vestibular feedback during the sub-acute stage of recovery, which may also prove to be a reliable measure of progression in vestibular rehabilitation protocols.

Retro-labyrinthine Lesion Site Detected by Galvanic Vestibular Stimulation Elicited Vestibular-evoked Myogenic Potentials in Patients with Auditory Neuropathy.

OBJECTIVE: Auditory neuropathy (AN) is a unique pattern of hearing loss with preservation of hair cell function. The condition is characterized by the presence of otoacoustic emissions (OAE) or cochlear microphonic (CM) responses with severe abnormalities of the auditory brainstem response (ABR). The vestibular branches of the VIII cranial nerve and the structures innervated by it can also be affected. However, the precise lesion sites in the vestibular system are not well characterized in patients with AN. METHODS: The air-conducted sound (ACS) vestibular-evoked myogenic potentials (VEMPs) and galvanic vestibular stimuli (GVS)-VEMPs were examined in 14 patients with AN. RESULTS: On examination of VEMPs (n=14, 28 ears), the absent rates of ACS-cervical VEMP (cVEMP), ACS-ocular VEMP (oVEMP), GVS-cVEMP, GVS-oVEMP and caloric test were 92.9% (26/28), 85.7% (24/28), 67.9% (19/28), 53.6% (15/28), and 61.5% (8/13), respectively. Impaired functions of the saccule, inferior vestibular nerve, utricle, superior vestibular nerve, and horizontal semicircular canal were found in 25.0% (7/28), 67.9% (19/28), 32.1% (9/28), 53.6% (15/28) and 61.5% (8/13) patients, respectively. On comparing the elicited VEMPs parameters of AN patients with those of normal controls, both ACS-VEMPs and GVS-VEMPs showed abnormal results in AN patients (such as, lower presence rates, elevated thresholds, prolonged latencies, and decreased amplitudes). CONCLUSION: The study suggested that patients with AN often have concomitant vestibular disorders. Retro-labyrinthine lesions were more frequently observed in this study. GVS-VEMPs combined with ACS-VEMPs may help identify the lesion sites and facilitate detection of areas of vestibular dysfunction in these patients.

Transient Vestibular Symptoms Preceding Posterior Circulation Stroke: A Prospective Multicenter Study.

BACKGROUND AND PURPOSE: The recognition of clinical features of transient vestibular symptoms (TVSs) preceding posterior circulation stroke (PCOS) would be informative to discriminate dizziness/vertigo due to vertebrobasilar transient ischemic attack from the acute transient vestibular syndrome. We sought to determine the prevalence and characteristics of TVSs preceding PCOS. METHODS: We performed a prospective multicenter observational study that had recruited 447 patients with PCOS from referral-based 4 university hospitals in Korea. We investigated the timing, pattern, frequency, duration, and accompanying neurological symptoms of TVSs during the 3 months preceding PCOS. RESULTS: The prevalence of TVSs preceding PCOS was 12% (55/447) during the previous 3 months. The TVSs preceding PCOS occurred within 1 week (33%), between 1 week and 1 month (16%), or between 1 and 3 months (51%). The TVSs were mostly dizziness/vertigo with (36%) or without (60%) imbalance, while the remaining 4% had an isolated imbalance. The dizziness/vertigo was spinning in 38% and was aggravated during head position in 45%. The duration of TVSs was mostly a few seconds (55%) or minutes (38%). Approximately 72% of the patients with PCOS had TVSs 1 to 5 times, while 16% had >10 times. Accompanying neurological symptoms, including headache, tinnitus, limb weakness, sensory change, dysarthria, visual field defect, and diplopia, were reported in 11%. CONCLUSIONS: Preceding TVSs can occur in 12% of PCOS during the previous 3 months. Isolated dizziness/vertigo of unknown cause needs to be considered as a vertebrobasilar transient ischemic attack symptom, especially in patients with vascular risk factors. The characteristics of isolated vestibular symptom in vertebrobasilar transient ischemic attacks is highly variable and atypical compared with other transient ischemic symptoms.