Bilateral Vestibulopathy

Definition and epidemiology

Bilateral vestibulopathy (bilateral vestibular hypofunction) is a chronic vestibular syndrome caused by combined loss of function of the right and left labyrinths or vestibular nerves. The core deficit is bilateral reduction or loss of the vestibulo-ocular reflex (VOR), which keeps the image stable on the retina during head movement. The Bárány Society 2017 criteria base the diagnosis on symptoms and quantitative measurement of the VOR; cases meeting all criteria are classed as “bilateral vestibulopathy”, and those supported only by a bedside head impulse test as “probable bilateral vestibulopathy” (Strupp et al., 2017).

Onset can be sudden (for example after aminoglycoside treatment or meningitis) or slowly progressive, and both sides may be affected at once or one after the other. Milder, age-related bilateral loss of vestibular function is a separate diagnosis, covered in the presbyvestibulopathy entry.

Data from the 2008 US National Health Interview Survey put the adult prevalence at 28 per 100,000, roughly 64,000 people (Ward et al., 2013). Various reports give a relative incidence of 4-7% for bilateral vestibulopathy among vestibular disorders (Strupp et al., 2017). No population-based prevalence data for Türkiye were found.

Symptoms and signs

The main complaint is persistent unsteadiness when walking and standing. It becomes much worse in the dark, with the eyes closed and on uneven, soft or slippery ground, because the brain tries to replace vestibular input with vision and sensation from the soles of the feet. The absence of symptoms when sitting or lying still is part of the diagnosis (Strupp et al., 2017).

About 30-40% of patients describe the world bouncing, blurring or jumping when they walk or move the head quickly; this is called oscillopsia (Strupp et al., 2017). Patients may say they cannot read signs or recognise faces while walking, or that the view judders when travelling in a car. Because unsteadiness worsens in the dark, the risk of falls rises; difficulties with navigation and spatial memory are also reported.

Additional symptoms depend on the cause: attacks and fluctuating hearing in Ménière’s disease, profound hearing loss after meningitis, and sensory loss in the hands and feet, clumsiness and chronic cough in CANVAS. In one series 36% of patients had asymmetric hearing loss between the ears (Lucieer et al., 2016). Congenital bilateral vestibular loss, for example in Usher syndrome type 1, delays motor milestones such as head control and walking.

Causes and risk factors

No cause is found in a substantial proportion of patients. In a series of 255 patients the commonest identifiable causes were ototoxic drugs (13%), bilateral Ménière’s disease (7%) and meningitis (5%) (Zingler et al., 2007). In a more recent Dutch series of 154 patients, 31% were idiopathic; identified causes included genetic factors in 17%, Ménière’s disease in 16%, ototoxicity in 12%, infection in 6% and neurodegenerative disease in 4%. Half of the idiopathic group had a history of migraine (Lucieer et al., 2016).

Gentamicin is the leading ototoxic cause. Because it damages vestibular hair cells more than cochlear ones, balance function can be lost while hearing stays normal; this is covered in detail in the ototoxicity entry. Other causes include meningitis and labyrinthitis, autoimmune inner ear disease and Cogan syndrome, bilateral vestibular schwannomas in NF2-related schwannomatosis, superficial siderosis and bilateral labyrinthine concussion (Strupp et al., 2017).

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) is an important cause of late-onset ataxia and is associated with a biallelic intronic repeat expansion in the RFC1 gene (Cortese et al., 2019). In some series CANVAS was found in 10-20% of patients with bilateral vestibulopathy (Strupp et al., 2017). Neurological assessment is therefore important, particularly in older patients with sensory loss or clumsiness.

Audiological and clinical assessment

Under the Bárány Society criteria, four conditions must be met together (Strupp et al., 2017):

• A. Chronic vestibular syndrome: unsteadiness when walking or standing, plus blurred vision or oscillopsia during walking or quick head and body movements and/or worsening unsteadiness in the dark or on uneven ground.
• B. No symptoms while sitting or lying down under static conditions.
• C. Documented bilaterally reduced or absent VOR function: bilateral horizontal VOR gain below 0.6 on the video head impulse test (vHIT) or scleral coil; or a caloric response in which the sum of the bithermal maximum peak slow-phase velocities is below 6°/s on each side; or horizontal VOR gain below 0.1 on sinusoidal rotational testing (0.1 Hz) with a phase lead above 68 degrees (time constant below 5 seconds).
• D. Not better accounted for by another disease.

Bilateral catch-up saccades on the bedside head impulse test are enough for “probable bilateral vestibulopathy”. On vHIT, reduced gain is seen on both sides with overt and covert catch-up saccades. Because caloric testing assesses very low-frequency and vHIT and rotational testing higher-frequency head movement, the results do not always agree; in one series the head impulse test was abnormal in 94% of patients (Lucieer et al., 2016). Vestibular evoked myogenic potentials (VEMP) can show otolith involvement but are not part of the diagnostic criteria.

In the audiological assessment, pure tone and speech audiometry can point to the cause: high-frequency loss in ototoxicity, fluctuating low-frequency loss in Ménière’s disease and severe sensorineural loss after meningitis. On examination, the Romberg test is expected to fail, especially on foam with the eyes closed, and dynamic visual acuity is reduced. The differential diagnosis includes cerebellar ataxia, polyneuropathy, drug side effects, orthostatic hypotension and Persistent Postural-Perceptual Dizziness (PPPD); neurological examination and, where needed, brain MRI and nerve conduction studies are requested.

Treatment and audiological rehabilitation

There is no established treatment that restores lost vestibular function; management rests on addressing the cause, vestibular rehabilitation and preventing falls. Decisions such as whether to continue an ototoxic drug or how to treat Ménière’s or autoimmune disease are for the physician. Reviewing sedatives and vestibular suppressants that may worsen balance is part of this process.

Vestibular rehabilitation is the cornerstone of treatment. The updated guideline of the Academy of Neurologic Physical Therapy recommends vestibular rehabilitation for adults with bilateral hypofunction on the basis of strong evidence and highlights supervised programmes. For bilateral hypofunction it suggests gaze stabilisation exercises 3-5 times a day, totalling 20-40 minutes daily, for about 5-7 weeks, and advises against eye-only exercises without head movement for this purpose (Hall et al., 2022). Programmes include gaze stabilisation exercises that use any remaining vestibular function, sensory substitution strategies such as saccades and the cervico-ocular reflex, and balance and gait training that uses visual and somatosensory cues. Recovery in bilateral loss is slower and more limited than in unilateral loss, and goals should be set accordingly.

The vestibular implant is still experimental. In a study of eight adults with bilateral vestibular hypofunction who received a unilateral vestibular implant, posture, gait and quality-of-life measures improved; however, hearing in the implanted ear declined in all but one participant, markedly so in three (Chow et al., 2021). The vestibular implant is therefore not a routine treatment today and is offered only within clinical studies.

Associated sensorineural hearing loss is managed with hearing aids or a cochlear implant. Because poor hearing combined with poor balance makes communication and auditory awareness of the surroundings harder, hearing rehabilitation should be considered alongside the aim of reducing falls.

Impact on quality of life and advice

Bilateral vestibulopathy can markedly restrict daily life. Unsteadiness that worsens in the dark raises the risk of falls (Strupp et al., 2017). In US national survey data, 44% of adults with bilateral vestibular loss reported having stopped driving or changed their driving habits (Ward et al., 2013). Because there is nothing visible to see, others may not understand the symptoms, which can contribute to anxiety and depressive symptoms.

Practical advice: use lights to illuminate your way at night, remove slippery rugs and obstacles, and fit grab rails in the bathroom. A walking stick or frame increases safety in the dark and on uneven ground. Do not swim alone, because orientation can be lost underwater or in the dark. Driving, particularly at night and in heavy traffic, should be discussed with your team. Regular walking and exercise help the remaining sensory systems adapt.

Self-report questionnaires such as the Dizziness Handicap Inventory, the Activities-specific Balance Confidence Scale and the Vestibular Disorders Activities of Daily Living Scale can be used to track progress during rehabilitation.