Bilateral Vestibulopathy

1. 0:00Bilateral vestibulopathy is the textbook indication for the DVA test. It is the disease in which DVA earns its keep more than any other vestibular condition — and the only one in which a normal subjective visual vertical paradoxically coexists with profound vestibular impairment.
2. 0:25The Bárány Society defines bilateral vestibulopathy as a chronic vestibular syndrome with unsteadiness when walking or standing, worse in darkness or on uneven ground, and head-motion-induced blurred vision or oscillopsia. Crucially, there are no symptoms while sitting or lying still. The complaint is dynamic.
3. 0:55Quantitatively, the diagnosis requires bilaterally impaired or absent VOR. The thresholds: horizontal vHIT gain below 0.6 on both sides; or the sum of caloric peak slow-phase velocities less than six degrees per second per side; or rotational chair gain below 0.1 at 0.1 hertz. Any of these is sufficient. A bilaterally pathological bedside head impulse test alone defines probable bilateral vestibulopathy.
4. 1:30DVA is listed as a complementary test. The Bárány criteria specify a DVA loss of at least 0.2 logMAR — two chart lines — as pathological. In practice, severe bilateral vestibulopathy produces DVA losses of half a logMAR or more.
5. 2:00Why is the asymmetry pattern unusual? Because there is no asymmetry. Both sides are equally affected. The right-versus-left directional difference — the criterion most labs use to flag a unilateral DVA finding — is zero. Both directions are equally bad. This is one of the few clinical scenarios in which a normal directional asymmetry index is itself the diagnostic clue.
6. 2:35Aetiology is most commonly aminoglycoside ototoxicity — gentamicin is the worst offender — followed by sequelae of meningitis, bilateral Ménière's disease, and the CANVAS syndrome of cerebellar ataxia, neuropathy, and vestibular areflexia. About half remain idiopathic.
7. 3:00Recovery of vestibular function is uncommon. But DVA recovers with vestibular rehabilitation, primarily through the brain learning to deploy centrally-programmed compensatory saccades during head motion — covert saccades — even when VOR gain does not improve. DVA is therefore the right outcome measure for monitoring rehabilitation in this population.

What is bilateral vestibulopathy?

Bilateral vestibulopathy (BVP) is a chronic syndrome in which both inner ears have lost their vestibular function — or so much of it that the vestibulo-ocular reflex can no longer keep gaze stable during head motion. Patients are typically symptom-free at rest, and their complaints emerge only with movement.²⁴

The two cardinal symptoms are unsteadiness walking or standing — worse in darkness or on uneven ground, where the patient cannot use vision or proprioception to compensate — and oscillopsia, the experience of the world moving on the retina during head motion. Patients describe it as the print jumping while they read, signs blurring as they walk, or the inability to recognise faces from a moving car.^24,27

How common is it?

Bilateral vestibulopathy is uncommon. The Ward 2013 analysis of the US National Health Interview Survey estimated a population prevalence of approximately 28 per 100,000 adults.²⁷ In tertiary dizziness clinics it accounts for roughly 1% of new referrals. The condition is associated with falls, reduced functional independence, and a high disease burden.²⁷

Bárány Society diagnostic criteria

The 2017 Bárány Society consensus defines BVP as the combination of clinical features above plus laboratory evidence of bilaterally impaired or absent VOR. The quantitative thresholds are reproduced below, drawn from the consensus document.²⁴

• vHIT or scleral coil:horizontal aVOR gain < 0.6 on both sides at angular velocity 150–300°/s, and/or
• Bithermal caloric test:sum of maximal slow-phase velocities (warm + cold) < 6°/s on each side, and/or
• Rotational chair:horizontal aVOR gain < 0.1 at 0.1 Hz sinusoidal stimulation (V_max 50°/s), and/or phase lead > 68° (time constant < 5 s).

Any one of these thresholds, in the presence of the cardinal symptoms, is sufficient for the diagnosis. Probable BVP is defined by the cardinal symptoms plus a bilaterally pathological bedside head-impulse test.²⁴

DVA appears in the criteria as a complementary test: a DVA decrease of ≥0.2 logMAR is considered pathological. cVEMP, oVEMP, and the Romberg are mentioned but not included in the definition. The consensus is careful to note that DVA documents the functional consequence of the VOR loss rather than the loss itself.²⁴

Aetiology

The single most commonly identified cause is aminoglycoside ototoxicity — gentamicin in particular, with streptomycin, tobramycin, and amikacin following. Aminoglycoside vestibulotoxicity can be profound and irreversible; it characteristically spares hearing initially while devastating both vestibular ends.²⁶

Other recognised causes include bilateral Ménière's disease, meningitis (bacterial or carcinomatous) with bilateral labyrinthine involvement, autoimmune inner ear disease, bilateral vestibular schwannomas (NF2), the CANVAS syndrome (cerebellar ataxia, neuropathy, vestibular areflexia syndrome), and head trauma. Approximately half of cases remain idiopathic; in these, a neurodegenerative process is presumed.^24,26

The DVA pattern in detail

In bilateral vestibulopathy, DVA loss is large and the directional asymmetry is small. This is the inverse of unilateral vestibulopathy, where the asymmetry between rightward and leftward head motion is often the most striking finding while the absolute loss may be modest after compensation.

Two clinical implications follow. First, an asymmetry-based screening rule will miss bilateral vestibulopathy. Labs that flag only right-vs-left differences of ≥0.1 logMAR will report this patient as normal. Absolute DVA loss against the age-matched normative mean is the right criterion in this population.^21,24

Second, the magnitude of DVA loss can be large enough that the standard chart "floor" interferes. A patient losing six lines bilaterally cannot identify any optotype on a typical chart during oscillation. In severely affected patients, the test is reported as "no optotypes identified" rather than a quantitative logMAR — but this is itself a positive finding.

Why the SVV is normal

A patient with profound bilateral vestibulopathy may present with a completely normal subjective visual vertical. This is sometimes mistaken for evidence against the diagnosis. It is not.

SVV measures the asymmetry between the two graviceptive inputs. When both utricles fail symmetrically, the asymmetry is zero and the SVV is therefore normal. The patient is still profoundly impaired; the test is simply the wrong tool for symmetric bilateral loss. DVA and the head-impulse test detect what the SVV cannot.²⁴

Rehabilitation and the DVA outcome measure

Vestibular function in established BVP rarely recovers — peripheral hair cells do not regenerate in humans, and central compensation has fewer asymmetry signals to work with than in unilateral loss. Yet DVA does improve with rehabilitation.²⁵

Herdman and colleagues (2007) randomised thirteen BVP patients to structured gaze-stabilisation exercises versus placebo. The exercise group showed significant DVA improvement; the placebo group did not. Slow-phase eye velocity gain did not change in most patients — arguing strongly that improvement is mediated not by VOR-gain recovery but by the brain learning to deploy centrally- programmed compensatory saccades during head motion. Covert catch-up saccades, when well-timed, can preserve dynamic acuity even in the absence of a functioning reflex.^5,25

The clinical implication: DVA is the right outcome measure to track rehabilitation in BVP, even though caloric and vHIT results do not change. A loss reduction of 0.1 logMAR (one chart line) over four to six weeks of structured exercise is a typical responder pattern. Use the same paradigm at each visit — bedside scores are not interchangeable with computerised scores.^5,25

Differential diagnosis

The principal differential is between BVP and other syndromes that produce oscillopsia or unsteadiness:

• Cerebellar disease — typically produces gaze-evoked nystagmus, dysmetric saccades, and impaired smooth pursuit. DVA may be abnormal centrally rather than peripherally; vHIT is often preserved.¹⁶
• Sensory ataxia from large-fibre neuropathy — unsteadiness worsens in darkness as in BVP, but the head-impulse test, DVA, and caloric responses are all normal. Romberg is markedly positive; vibration sense is impaired.
• Presbyvestibulopathy — milder version of the same picture in older adults, by definition with bilaterally reduced but not absent vestibular function. The 2019 Bárány criteria for presbyvestibulopathy use a less severe vHIT-gain threshold than BVP.
• CANVAS — the cerebellar ataxia + sensory neuronopathy + vestibular areflexia syndrome. The vestibular picture is identical to other BVP; the cerebellar and neuropathic features distinguish it. Look for chronic cough, an early CANVAS clue.²⁶

Reading the report

A bilaterally symmetric DVA loss of ≥0.4 logMAR with bilaterally abnormal vHIT and caloric responses is sufficient for the diagnosis when the cardinal symptoms are present. The clinician should then pursue aetiology with a careful drug history (aminoglycosides including past gentamicin or chemotherapy with platin agents), screening audiometry, and — when the gait or neurological examination is atypical — neuroimaging and CANVAS screening (RFC1 expansion testing where available).^24,26