Making the diagnosis
Differential diagnosis
The complaint — chronic unsteadiness, worse in the dark — is shared by several disorders. Bilaterally reduced vestibular testing with oscillopsia is what sets this one apart.
What else causes chronic imbalance
Other conditions also make people unsteady. A one-sided balance loss causes spinning at first. Problems in the cerebellum (the brain’s balance coordinator) add slurred speech and clumsy limbs. Loss of feeling in the feet causes unsteadiness too. And some people have persistent dizziness with completely normal balance tests.
Key separators: a unilateral deficit is asymmetric (spinning at onset, one positive head impulse). A cerebellar/central disorder adds gaze-evoked or downbeat nystagmus, abnormal pursuit and saccades, and limb ataxia. A sensory neuropathy gives a markedly positive Romberg with reduced vibration sense but normal vestibular tests. Functional dizziness (PPPD) has normal testing and no oscillopsia.1
The important overlap to recognise is CANVAS, in which bilateral vestibulopathy, cerebellar ataxia and a sensory neuropathy coexist — so “central signs” do not exclude BVP, they may define a specific cause.2 When testing is equivocal, repeat across frequencies before attributing the picture to a non-vestibular cause.3
Bilateral vestibulopathy against its mimics
Bilateral vestibulopathy is the reference row; tap a mimic to surface the discriminator.
Tap a mimic to reveal the discriminator. Bilaterally reduced testing with oscillopsia is the key.
When to reconsider
Spinning vertigo with a single positive head impulse points to a unilateral vestibulopathy; gaze-evoked or downbeat nystagmus and limb ataxia to a central/cerebellar disorder; persistent dizziness with normal testing to PPPD. Where ataxia and a neuropathy accompany the vestibular loss, think CANVAS and pursue the genetic work-up.
Key points
- Unilateral loss is asymmetric (spinning, one positive head impulse) — not bilateral failure.
- Cerebellar/central disease adds central oculomotor signs and limb ataxia; sensory ataxia gives a positive Romberg with normal vestibular tests.
- Functional dizziness (PPPD) has normal vestibular testing and no oscillopsia.
- CANVAS combines BVP, cerebellar ataxia and neuropathy — central signs may point to a cause, not away from BVP.