Functional Testing of Vestibulo-Spinal Contributions to Balance Control: Insights From Tracking Improvement Following Acute Bilateral Peripheral Vestibular Loss

Bilateral vestibulopathy and disabling vertigo: A CARE case series

INTRODUCTION

The term bilateral vestibulopathy (BV) was recently defined by the Bárány Society. Loss of otolith function was not included in their criteria. Although spontaneous progression to complete bilateral impairment of vestibular function is expected, it is unlikely that patients with advanced BV will continue to present episodes of intense vertigo. Here, following CARE case report guidelines, we report the case of patients meeting the criteria for BV and still disabled by vertigo.

CASE SERIES

Three patients evaluated in our department meeting the Bárány criteria for definite BV but still complaining of disabling rotatory vertigo were included. All underwent clinical and instrumental vestibular examination. The observations are reported.

CONCLUSION

In case of BV, the conservation of a stable otolithic reference frame could allow patients to optimize postural strategy. It would be useful to revisit a classification of BV by stages, by introducing an evaluation of otolithic function and postural control for possible subsequent vestibular implantation.

Vestibular Rehabilitation for Peripheral Vestibular Hypofunction: An Updated Clinical Practice Guideline From the Academy of Neurologic Physical Therapy of the American Physical Therapy Association

Background:

Uncompensated vestibular hypofunction can result in symptoms of dizziness, imbalance, and/or oscillopsia, gaze and gait instability, and impaired navigation and spatial orientation; thus, may negatively impact an individual's quality of life, ability to perform activities of daily living, drive, and work. It is estimated that one-third of adults in the United States have vestibular dysfunction and the incidence increases with age. There is strong evidence supporting vestibular physical therapy for reducing symptoms, improving gaze and postural stability, and improving function in individuals with vestibular hypofunction. The purpose of this revised clinical practice guideline is to improve quality of care and outcomes for individuals with acute, subacute, and chronic unilateral and bilateral vestibular hypofunction by providing evidence-based recommendations regarding appropriate exercises.

Methods:

These guidelines are a revision of the 2016 guidelines and involved a systematic review of the literature published since 2015 through June 2020 across 6 databases. Article types included meta-analyses, systematic reviews, randomized controlled trials, cohort studies, case-control series, and case series for human subjects, published in English. Sixty-seven articles were identified as relevant to this clinical practice guideline and critically appraised for level of evidence.

Results:

Based on strong evidence, clinicians should offer vestibular rehabilitation to adults with unilateral and bilateral vestibular hypofunction who present with impairments, activity limitations, and participation restrictions related to the vestibular deficit. Based on strong evidence and a preponderance of harm over benefit, clinicians should not include voluntary saccadic or smooth-pursuit eye movements in isolation (ie, without head movement) to promote gaze stability. Based on moderate to strong evidence, clinicians may offer specific exercise techniques to target identified activity limitations and participation restrictions, including virtual reality or augmented sensory feedback. Based on strong evidence and in consideration of patient preference, clinicians should offer supervised vestibular rehabilitation. Based on moderate to weak evidence, clinicians may prescribe weekly clinic visits plus a home exercise program of gaze stabilization exercises consisting of a minimum of: (1) 3 times per day for a total of at least 12 minutes daily for individuals with acute/subacute unilateral vestibular hypofunction; (2) 3 to 5 times per day for a total of at least 20 minutes daily for 4 to 6 weeks for individuals with chronic unilateral vestibular hypofunction; (3) 3 to 5 times per day for a total of 20 to 40 minutes daily for approximately 5 to 7 weeks for individuals with bilateral vestibular hypofunction. Based on moderate evidence, clinicians may prescribe static and dynamic balance exercises for a minimum of 20 minutes daily for at least 4 to 6 weeks for individuals with chronic unilateral vestibular hypofunction and, based on expert opinion, for a minimum of 6 to 9 weeks for individuals with bilateral vestibular hypofunction. Based on moderate evidence, clinicians may use achievement of primary goals, resolution of symptoms, normalized balance and vestibular function, or plateau in progress as reasons for stopping therapy. Based on moderate to strong evidence, clinicians may evaluate factors, including time from onset of symptoms, comorbidities, cognitive function, and use of medication that could modify rehabilitation outcomes.

Discussion:

Recent evidence supports the original recommendations from the 2016 guidelines. There is strong evidence that vestibular physical therapy provides a clear and substantial benefit to individuals with unilateral and bilateral vestibular hypofunction.

Limitations:

The focus of the guideline was on peripheral vestibular hypofunction; thus, the recommendations of the guideline may not apply to individuals with central vestibular disorders. One criterion for study inclusion was that vestibular hypofunction was determined based on objective vestibular function tests. This guideline may not apply to individuals who report symptoms of dizziness, imbalance, and/or oscillopsia without a diagnosis of vestibular hypofunction.

Disclaimer:

These recommendations are intended as a guide to optimize rehabilitation outcomes for individuals undergoing vestibular physical therapy. The contents of this guideline were developed with support from the American Physical Therapy Association and the Academy of Neurologic Physical Therapy using a rigorous review process. The authors declared no conflict of interest and maintained editorial independence.

Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A369).

Vestibular contributions to the Romberg test: Testing semicircular canal and otolith function

Normal stance relies on three sensory inputs: vision, proprioception and vestibular function. The Romberg test, trying to stand with feet together and eyes closed, is familiar to every medical student as a test of distal proprioceptive impairment. It remains the best known of Romberg's many remarkable contributions to clinical neurology. In Romberg's time almost nothing was known about the function of the vestibular system. We now know that standing with the eyes closed on a compliant rather than a firm surface is more a test of vestibular than proprioceptive function. Peripheral vestibular function tests in clinical use today all rely on measurements of oligosynaptic brainstem reflexes. Short-latency eye rotations in response to rapid, brief head rotations (head impulses) give an accurate, robust and reproducible measure of the function of any and each of the six semicircular canals. Short-latency evoked potentials from sternomastoid and inferior oblique muscles in response to loud clicks or skull taps (vestibular evoked myogenic potentials) give an accurate and reproducible measure of the function of each and any of the four otolith organs. In the present paper, we briefly review what is now known about the anatomy and physiology of the peripheral receptors and brainstem pathways mediating these reflexes and examine how this knowledge can help interpret the Romberg test.

5-HT1A receptor-mediated attenuation of synaptic transmission in rat medial vestibular nucleus impacts on vestibular-related motor function

KEY POINTS

Chemogenetic activation of medial vestibular nucleus-projecting 5-HT neurons resulted in deficits in vestibular-mediated tasks, including negative geotaxis, balance beam and rota-rod tests. The 5-HT_1A receptor mediates the vestibular-related behavioural effects of 5-HT in the vestibular nucleus. 5-HT_1A receptor activation attenuated evoked excitatory postsynaptic currents and evoked inhibitory postsynaptic currents via a presynaptic mechanism in the vestibular nucleus.

ABSTRACT

While the anxiolytic effects of serotonergic neuromodulation are well studied, its role in sensorimotor coordination and postural control is unclear. In this study, we show that an increase of serotonin (5-hydroxytryptamine, 5-HT) at the medial vestibular nucleus (MVN), a brainstem centre for vestibulospinal coordination, by either direct cannula administration or chemogenetic stimulation of MVN-projecting serotonergic neurons, adversely affected performance of rats in vestibular-mediated tasks, including negative geotaxis, balance beam and rota-rod tests. Application of the 5-HT₁ and 5-HT₇ receptor co-agonist 8-hydroxy-2-(di-n-propylamino) tetralin recapitulated the effect of 5-HT, while co-administration of the specific 5-HT_1A receptor antagonist WAY 100135 effectively abolished all 5-HT-induced behavioural deficits. This indicated that 5-HT_1A receptors mediated the effects of 5-HT in the rat MVN. Using whole-cell patch-clamp recording, we demonstrated that 5-HT_1A receptor activation attenuated both evoked excitatory and evoked inhibitory postsynaptic currents through a presynaptic mechanism in the rat MVN. The results thus highlight the 5-HT_1A receptor as the gain controller of vestibular-related brainstem circuits for posture and balance.

How sacculo-collic function assessed by cervical vestibular evoked myogenic Potentials correlates with the quality of postural control in hearing impaired children?

OBJECTIVE

Functional integrity of vestibular end organs is essential for gaze stabilization, dynamic visual acuity, postural control and spatial orientation. Some authors hypothesized on the importance of saccules for postural control and motor development in children, including achievements such as standing up and walking. The purpose of this article was to observe how saccular dysfunction assessed by cervical Vestibular Evoked Myogenic Potentials (cVEMPs) correlates with the quality of postural control in non-syndromic deaf children.

METHOD

Seventy-six non-syndromic hearing-impaired children were retrospectively included. Sacculo-collic pathway was assessed with cVEMPs elicited in bone conduction. The response was quoted "normal" if a reproducible wave P13-N23 of at least 50μV in amplitude was present, if not, it was quoted "absent". The sample was divided in 3 groups depending on the presence of the sacculo-collic responses: normal bilateral group (Group 1), normal unilateral (Group 2) and absent bilaterally group (Group 3). Motor assessment was achieved with Movement Assessment Battery for Children, second edition (MABC-2). Postural control (PC) was assessed using the dynamic Balance Quest platform. The scores obtained with MABC-2, and the postural parameters recorded on the Balance Quest platform (sway of Centre of Pressure and spectral power index) were analyzed and compared throughout the groups.

RESULTS

Group 1 (normal bilateral) showed the best scores regarding motor abilities and postural stability within available normative data. Group 3 (absent bilateral) had the lowest motor and postural control skills. A good correlation between the scores obtained by MABC-2 motor test and dynamic posturography (Balance Quest) was observed.

CONCLUSIONS

The presence of at least one sacculo-collic response would predict satisfactory static and dynamic motor and postural control skills in non-syndromic hearing-impaired children. MABC-2 and Dynamic Posturography Balance Quest appears reliable and comparable tools for PC assessment in hearing impaired children. In the light of these results, it appears that in young children candidates for uni- or bilateral CI whose walking is not yet acquired, should receive a vestibular assessment before surgery to avoid the risk of bilateral sacculo-collic function impairment.