Diseases and Disorders

Bilateral Vestibular Hypofunction

Priya Vijayakumar


Introduction

Bilateral vestibular hypofunction (BVH) is broadly characterized by the inability to maintain posture and balance, walk in environments with low visibility, and see clearly during head movements [1]. The effects of the disorder are due to decreased vestibular function in the inner ear [2].  BVH was first described by neurosurgeon Dr. Walter Dandy in 1941 [3]. After performing a series of bilateral vestibular neurectomies on patients with Meniere’s Disease, Dandy observed symptoms of oscillopsia and imbalance in the absence of light [4]. The next seventy-five years were significant in demystifying the varying causes for BVH and developing innovative  therapies to treat the disorder.

 

Symptoms

    Although symptoms vary among patients, a few are clinically recognized as hallmark indications of BVH. Oscillopsia is the result of reductions in the vestibulo-ocular reflex; eye-movements cohere to head movements rather than stabilizing in opposition to head movements. Due to oscillopsia, blurring of vision produces visual vertigo and causes imbalance which can lead to excessive falling. In the elderly population, falling can be especially dangerous as it is the leading cause of accidental death for people aged 65 and older [1]. On top of these keystone symptoms of BVH, patients may also exhibit cognitive deficits such as difficulties concentrating due to dizziness and disorienting visual environments [3].      

 

Etiology

    The majority of BVH cases are idiopathic with heterogeneous origins.  Ototoxicity accounts for nearly 50% of BVH cases [5]. Also, the consumption of Gentamicin, a common antibiotic, is widely linked to inducing BVH. Recent research suggests a possible correlation between free radical generation and the development in the BVH as well [6]. The onset of BVH is often triggered by primary infections, disorders, or diseases such as Meniere’s Disease, meningitis, autoimmune disorders, chronic inflammatory peripheral neuropathy, and deafness. Furthermore, aging is widely implicated in the development of BVH beyond the age of 80 due to a 50% decrease in the vestibular neuron population [1][6].

 

Courtesy of http://www.physiotherapyvictoria.ca/

 

Diagnosis

    Due to the idiopathic nature of BVH, diagnosing the disorder is challenging and in most cases, evades clinical diagnosis. Regardless, four methods are most effective in confirming BVH: the head impulse test, the dynamic visual acuity test, the Romberg test and ophthalmoscopy. During the head impulse test, an examiner manually rotates the patient’s head while he or she is in a sitting position. While a patient without BVH stabilizes focus on the examiner, a patient with BVH exhibits drifting eyes. Similarly, testing for dynamic visual acuity also involves oscillating the patient’s head; however, the patient must also read optotypes. Although it is normal to misread a few lines of optotypes, patients with BVH demonstrate a severe inability to accurately read them. The Romberg test assesses postural control; patients stand with their feet together, typically on a piece of foam, with their eyes closed. If the patient sways or falls, then this response indicates an abnormality in proprioception. Typically, the head impulse test, testing for dynamic visual acuity, and the Romberg test are performed together and do not require a clinical setting. Perhaps the most straightforward test is ophthalmoscopy which entails dilating the pupils and examining the back of the eyes for abnormalities [7].

Observations of daily functioning is also fruitful in diagnosing BVH. If the patient experiences dizziness during sudden movement, is unable to drive at night, or is unable to play sports, then a visit to the clinic for a potential diagnosis might be necessary [2].

 

Therapy

    The most common treatment for BVH is compensatory therapy in which the patient exercises gaze stabilization or maintenance of posture to supplement decreased vestibular function. Given the effectiveness of cochlear implants, current research is developing vestibular prosthesis that are designed to detect head maneuvers and accordingly, stimulate ampullary nerves. Thus far, this development has been proven to work and is continuing to improve [1].

 

Key Terms:

Bilateral vestibular neurectomy - A surgical procedure that cuts or removes the vestibular nerve

Meniere’s Disease - A progressive disease causing deafness, vertigo and tinnitus.

Oscillopsia - Visual disturbances  in which objects appear to oscillate

Ototoxicity- Toxicity caused by chemicals or drugs to the inner ear

Optotype - A chart with rows of letters and figures that is used to test visual acuity

Proprioception- The body’s coordinated awareness of its position

Ophthalmoscopy - An instrument used to inspect the eye


References


  1. Petersen, J. A., Straumann, D., & Weber, K. P. (2013). Clinical Diagnosis of Bilateral Vestibular Loss: Three Simple Bedside Tests. Retrieved October 24, 2016, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3526948/

  2. Bilateral Vestibulopathy. (n.d.). Retrieved October 24, 2016, from http://american-hearing.org/disorders/bilateral-vestibulopathy/

  3. Lucieer, F., Vonk, P., Guinand, N., Stokroos, R., Kingma, H., & Berg, R. V. (2016). Bilateral Vestibular Hypofunction: Insights in Etiologies, Clinical Subtypes, and Diagnostics. Frontiers in Neurology Front. Neurol., 7. doi:10.3389/fneur.2016.00026

  4. Gillespie, M. B., & Minor, L. B. (1999). Prognosis in Bilateral Vestibular Hypofunction. The Laryngoscope, 109(1), 35-41. doi:10.1097/00005537-199901000-00008

  5. Berg, R. V., Tilburg, M. V., & Kingma, H. (2015). Bilateral Vestibular Hypofunction: Challenges in Establishing the Diagnosis in Adults. Orl, 77(4), 197-218. doi:10.1159/000433549

  6. Schubert, M. C., & Minor, L. B. (2004, April). Vestibulo-ocular Physiology Underlying Vestibular Hypofunction. The Journal of the American Physical Therapy Association, 84(4). doi:84:373-385

  7. Bilateral Vestibular Hypofunction. (2015). Retrieved October 24, 2016, from https://vestibular.org/BVH

Priya Vijayakumar

Priya Vijayakumar


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