Bilateral Vestibular Hypofunction

Original Editor - Hillary Chong, Nadia Iantorno, Priyanka Kumar, Quinn Powell-Jones as part of the Queen's University Neuromotor Function Project
Top Contributors - Hillary Chong, Priyanka Kumar, Nadia Iantorno, Kim Jackson, Quinn Powell-Jones, Mariam Hashem and WikiSysop

Description

Bilateral vestibular hypofunction (BVH) is a heterogeneous condition that results from defects in either the vestibular organs, eighth cranial nerves, or a combination of the two. This condition causes impairments in the vestibulo-ocular reflex (VOR) and the major functions of the vestibular organs. As a result of the loss or diminished function, patients may present with imbalance, oscillopsia and impaired spatial orientation. Patients may also present with neurological and auditory symptoms, depending on the cause of their BVH. Prognosis is determined by the severity of this condition, which is dependent on the number of underlying comorbidities. Individuals with initial poor falls risk scores, lower balance confidence, and greater disequilibrium tend to have a poorer disability that may influence the functionality in everyday life. Due to the heterogeneity of the disease, BVH has four clinical subtypes:

1. Recurrent vertigo and BVH
2. Rapidly progressive BVH
3. Slowly progressive BVH
4. BVH with neurological deficits

Epidemiology

BVH is an uncommon condition that is frequently misdiagnosed or underdiagnosed. The reported prevalence of BVH in the literature ranges from 28 to 81 per 100 000 US adults, with greater prevalence seen in women and Hispanics. Individuals diagnosed with BVH are more likely to present with social, physical, and functional impairments and limitations.

Aetiology/Causes

BVH is often a secondary condition from a wide spectrum of causes as listed in Table 1 below. The majority of BVM cases, about 51%, are idiopathic in nature because an underlying cause cannot be identified. Of the known determinants, toxic/metabolic (13-21% of cases) is the most common and an example of this is ototoxicity, where the side effect of antibiotics, particularly aminoglycoside, results in persisting deficits (BVH). Other known causes may be the result of an infection (3.8-12%) such as meningitis, and encephalitis. 

Table 1: Etiologies of BVH

Idiopathic(51%)	-
Toxic/Metabolic           (13-21%)	Antibiotics, furosemide, cisplatin, aspirin, alcohol, vitamin B12 deficiency, folate deficiency, hypothyroidism, styrene poisoning, a combination of nonsteroidal anti-inflammatory drug plus penicillin
Infectious          (3.8-12%)	Meningitis/encephalitis/cerebellitis, lues, Behçet’s disease, Borrelia infection, herpes simplex virus infection, bilateral neuritis
Autoimmune             (10%)	Cogan’s syndrome, Susac’s syndrome, sarcoidosis, Granulomatosis with polyangiitis, Sjögren’s syndrome, colitis, celiac disease, polyarteritis nodosa, antiphospholipid syndrome, other systemic diseases
Neurodegenerative	CANVAS, superficial siderosis, episodic ataxia, multiple system atrophy, polyneuropathy, SCA3, SCA6, hereditary sensory and autonomic neuropathy type IV, other ataxias
Genetic	DFNA-9, DFNA-11, DFNA-15, DFNB-4, mutation chromosome 5q, 6q, 11q, 22q
Vascular	Supra- or infratentorial lesions, vertebrobasilar dolichoectasia
Neoplastic	Bilateral vestibular schwannoma, neurofibromatosis type 2, metastasis of lymphoma, malignant tumour
Trauma	Head trauma, iatrogenic (e.g. bilateral cochlear implantation)
Other ear pathology	Bilateral Meniere’s disease, otosclerosis, bilateral labyrinthitis, cholesteatoma
Congenital/syndromal	CHARGE, Usher, Turner, enlarged vestibular aqueduct, Alport syndrome
Other	Presbyvertigo, vestibular atelectasis, etc.
	SCA= Spinocerebellar ataxia; CHARGE= coloboma, heart defects, atresia of the choanae, retardation of growth and development, genital and urinary abnormalities, ear abnormalities and/or hearing loss.

Clinical Presentation

Common Symptoms of BVH:

• Oscillopsia
  Oscillopsia is visual blurring or oscillating of objects in an individual’s visual field while the head is in motion, and is experienced by 25-86% of patients with BVH. This reduces the vestibulo-ocular reflex, which is important in stabilizing gaze on stationary objects and maintain a motionless visual field as the head moves. In BVH, this deficit results in the eyes to move along with the head creating excessive motions of objects in the visual field even if stationary, which impairs vision.  Patients experiencing this may complain of blurred vision during movement or activities. Oscillopsia may increase with irregular or unpredictable head movements, such as head movements while walking. Inability to read street signs or identify people’s faces as they walk, or difficulty having clear sight while in a moving car may result. If severe, patients’ postural stability could be compromised due to a decreased ability to use visual cues for stability.
• Imbalance
  Patients with BVH typically complain of unsteadiness, imbalance, or a sense of “off-balance”, whether subtle or severe.  Postural control and orientation depends on proprioceptive, visual, and vestibular inputs and is disrupted in BVH due to failure of the vestibulospinal reflex. Therefore, patients present with decreased accuracy in gravity detection, and balance impairments during activities (walking in the dark or uneven surfaces, or any high-frequency head movements) have an increased risk of falling. Reduction in symptoms may be noticed when lying down, sitting with head support, and with avoidance of physical activities.
• Visual Vertigo
  Patients with BVH increase their visual dependence and use of visual inputs which may lead to visual vertigo. This is where symptoms (feeling off-balance, spinning, objects moving) are aggravated by visual contexts (moving objects, busy/crowded places, scrolling down on the computer screen, etc). Patients can experience abnormally large postural responses to visual environments with visual vertigo. 
• Cognitive Deficits
  Difficulty concentrating, fatigue, and being in a “brain fog” are some cognitive deficits that individuals with BVH may report. These symptoms may be the result of constant compensation, avoidance of imbalances, and attention to tasks such as walking, especially when paired with cognitive tasks (patients may stop walking if need to talk). Spatial learning and memory deficits result from absent labyrinthine input.
• Psychological or Psychiatric Symptoms
  Symptoms of chronic disequilibrium and difficulty performing activities of daily living can have psychological impacts. Particularly in the chronic phase (3+ months), psychiatric disorders (depression, somatic anxiety, etc.) have debilitating effects on the clinical picture and prognosis, therefore it is important healthcare providers take this into consideration when assessing and treating patients with BVH.
• Neurological Symptoms
  As stated above in Table 1: Etiology of BVH, BVH may be caused by neurological diseases (spinocerebellar ataxia, multiple system atrophy, etc.), infectious diseases (meningitis, encephalitis, etc.), vascular lesions, and other neurological conditions. Up to 39% of patients with BVH may have vestibular deficits combined with a neurological disorder.
• Autonomic Symptoms
  The vestibulosympathetic reflex projects to areas involved in the regulation of emotional aspects of vestibulo-autonomic function, and cardiorespiratory activity (breathing, heart rate and blood pressure). As such, orthostatic hypotension or autonomic symptoms may be the consequence of a disturbance between vertigo and panic.

Clinical pictures of the four different clinical subtypes:

1. Recurrent vertigo and BVH Patients experience episodic vertigo that may persist for several years and bilateral vestibular function loss symptoms. 
2. Rapidly progressive Rapid progression or sudden onset of BVH symptoms with or without episodes of vertigo.
3. Slowly progressive BVH Gradual development of symptoms, mainly without episodic vertigo.
4. BVH with neurological deficits Combination of BVH and neurological symptoms, such as peripheral polyneuropathy and/or cerebellar ataxia.

These four subtypes show broad clinical pictures and demonstrate that vertigo does not always have to be a symptom of BVH. Depending on patient symptoms (vertigo or hearing loss), medical assistance can be required early on in onset, however, if subtle or episodic in nature can lead to the delay in diagnosing this condition.

Diagnostic Procedures 

Currently, no standardized procedures are implemented for diagnosing BVH by healthcare professionals due to the challenges faced with diagnosing, since patients present with a broad spectrum of signs and symptoms. However, symptoms specific to, and commonly reported by patients include; oscillopsia (strong indicator of BVH), unsteadiness, episodic and spontaneous vertigo.

Vestibular tests performed to help diagnose BVH:

• Caloric Test
• Rotatory Chair Test
• Head Impulse Test (HIT)
• Vesitbular-Evoked Myogenic Potentials (VEMP)Dynamic Visual Acuity Test (DVA)
• Torsion Swing Test
  

Other tests conducted to aid in determining the cause:

• Cerebral imaging
• Audiometry
• Blood Tests

Differential Diagnosis

• Sarcoidosis
• Cerebellar syndrome
• Autoimmune inner ear disease
• Meningitis
• Sequential vestibular neuritis
• Neurofibromatosis type 2 with bilateral vestibular schwannomas,
• Bilateral Meniere’s disease
• Neurosyphilis
• Congenital malformations
• Cogan’s syndrome
• Post-binaural cochlear implantation
• Temporal bone fractures

Medical Management 

Management of patients in the acute phase involves the use of vestibular suppressants and anti-emetics. However, currently, the use of medications for chronic BVH is not supported by evidence.

Physiotherapy Management/Intervention

The management guidelines for patients with BVH varies according to the stage of the disorder. The original exercises developed by Cawthorne and Cooksey in the 1940’s outlined a general approach to vestibular rehab, which included a standardized series of exercises that involve eye movements without moving the head, head movements with eyes open or closed, bending over, sit-stand, tossing a ball, and walking. 

Current vestibular rehab involves an exercise based approach that incorporates four exercise components to address impairments and functional rehab:

1. Exercises to promote gaze stability (gaze stability exercises) Gaze stability exercises are referred to as substitution and adaptation exercises, which are performed in both sitting/standing upright and lying. Adaptation allows for long term changes in the nervous system and head movements when focusing on stationary or moving targets.
2. Exercises to habituate symptoms (habituation exercises) including optokinetic exercises Substitution exercises involve smooth pursuit eye movements to substitute for missing vestibular function. An example of substitution involves large eye movements towards a target before the head moves. Habituation exercises focuses on reducing vestibular symptoms through repeated, systematic exposure to specific stimuli that evoke dizziness. Optokinetic stimuli use repetitive movement patterns to decrease visual motion sensitivity. The patient’s training can be progressed by manipulating parameters such as velocity, direction, size, colour, and patient instructions. Other examples include virtual reality, busy screen savers or computer screens, and videos of busy visual environment.
3. Exercises to improve balance and gait (balance and gait training) These exercises use visual and somatosensory cues to substitute for missing vestibular function. Balance exercises involve balancing under different conditions of altered visual and/or somatosensory input. For example, the use of foam surfaces, moving platforms, and narrowing the base of support by standing in tandem or single leg stance.
4. Walking for endurance
   Walking for endurance or aerobic exercises is an element of rehab because people with peripheral vestibular dysfunction often limit physical activity to avoid provoking symptoms.

Outcome Measures 

Outcome measures are based on the International Classification of Functioning, Disability and Health Model.

Common outcome measures influencing the Body Structure and Function level:

• Dynamic Visual Acuity Test
• Sensory Organization Testing
• Dynamic Posturography

Common measures determining one’s ability to execute tasks in the Activities Classification level:

• Berg Balance Scale
• Dynamic Gait Index
• Timed Up and Go

Common measures that help determine Participation in society:

• The Activities-Specific Balance Scale
• Dizziness Handicap Inventory
• Other measures for Quality of Life such as the Vestibular Disorder Activities of Daily Living

Additional outcome measures for Body Structure and Function:

• Gait Stabilization Test
• Sharpened Romburg
• Sensory Organization Test with Head Shake, (Modified) Clinical Test of Sensory Interaction on Balance
• Visual Analogue Scale
• Visual Vertigo Analogue Scale
• Motion Sensitivity Quotient, and/or Vertigo Symptoms Scale

Additional outcome measures for Activity/Participation:

• Five Times Sit-to-Stand
• 30-Second Chair Stand
• Functional Reach/Modified Functional Reach
• Gait Velocity (10m Walk Test)
• Balance Evaluations Systems Test
• Mini Balance Evaluation Systems Test
• Modified Timed Up and Go with Dual Task
• Disability Rating Scale
• UCLA Dizziness Questionnaire
• Vertigo Handicap Questionnaire
• Vestibular Handicap Questionnaire
• Vestibular Activities and Participation
• Vestibular Rehabilitation Benefit Questionnaire

Resources 

Clinical Practice Guideline

Outcome measure reviews