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BPPV: which canal? Read the nystagmus
In BPPV, loose otoconia turn gravity into a canal stimulus. The direction of the nystagmus tells you which canal is involved, and that decides the manoeuvre.
- Recognise posterior, lateral and anterior canal BPPV from the nystagmus.
- Explain each pattern with Ewald’s laws, instead of memorising it.
- Spot features that point to a central cause instead.
What’s happening
Otoconia (calcium carbonate crystals) come loose from the utricle and drift into a semicircular canal. When the head moves into the provoking position, the particles sink, drag the endolymph with them and bend the cupula. The result is brief vertigo with nystagmus that starts after a few seconds’ delay (latency), lasts under a minute and settles with repetition (fatigue).
The posterior canal is by far the most often affected, because it’s the lowest part of the labyrinth when lying down.
The patterns at a glance
| Canal | How common | Test | Nystagmus | First-line treatment |
|---|---|---|---|---|
| Posterior | Most cases (about 80–90%) | Dix–Hallpike, affected ear down | Upbeating and torsional, top of the eyes beating towards the lower ear | Epley or Semont |
| Lateral, geotropic | About 10–15% (both forms) | Supine roll test | Horizontal, beating towards the ground on both sides; stronger with the affected ear down | Barbecue (Lempert) roll or Gufoni |
| Lateral, apogeotropic | Supine roll test | Horizontal, beating away from the ground on both sides; stronger with the healthy ear down | Gufoni (apogeotropic version) or converting it to the geotropic form | |
| Anterior | Rare (about 1–3%) | Dix–Hallpike or straight head-hanging | Downbeating, with little torsion | Deep head-hanging (Yacovino), after excluding a central cause |
Why the nystagmus looks like that
Posterior canal
In the Dix–Hallpike, particles fall away from the ampulla. In a vertical canal that’s excitatory (Ewald), so the fast phases beat up and twist towards the lower ear.
Lateral, geotropic
Particles sit in the long arm. Turning towards the affected ear moves them towards the ampulla: excitatory for a lateral canal, so the nystagmus is strongest on that side.
Lateral, apogeotropic
Particles are stuck to the cupula or sit near the ampulla, so the effect reverses: the nystagmus is strongest with the healthy ear down.
When it might not be BPPV
- No latency, or it doesn’t fatigue and persists while the position is held.
- Pure downbeat or pure torsional nystagmus, or nystagmus that doesn’t fit a single canal.
- Other neurological features: new headache, double vision, unsteady walking, slurred speech, or weakness.
Positional nystagmus with these features needs a neurological assessment and usually imaging.
Try it with your model: a right Dix–Hallpike
- Sit the model upright and turn the head 45° to the right.
- Lay it back so the head hangs about 20° below horizontal.
- Watch the right posterior canal: it now lies in the plane of the movement, with its long arm lowest, which is where loose particles settle, away from the ampulla.
- Continue the Epley steps and trace the particles’ path around the canal and out into the utricle.
- Upbeating and torsional on Dix–Hallpike: posterior canal, on the side of the lower ear.
- Horizontal on supine roll: lateral canal. Geotropic: the stronger side is affected. Apogeotropic: the weaker side is affected.
- Downbeating: consider the anterior canal, but rule out a central cause first.
- Typical BPPV has latency, lasts under a minute and fatigues.
Check yourself
Right Dix–Hallpike: after 4 seconds, upbeating torsional nystagmus with the top of the eyes beating to the right, fading in 20 seconds. Which canal?
Right posterior canal BPPV. Treat with a right Epley (or Semont).
Supine roll test: horizontal nystagmus beating towards the ground on both sides, stronger with the left ear down. Which side?
Left lateral canal, geotropic form. In geotropic lateral canal BPPV, the stronger side is the affected side.
Downbeating nystagmus in every head-hanging position, with no latency and no fatigue. BPPV?
Think central first. Persistent pure downbeat without latency or fatigue is a red flag for a central (often cerebellar) cause.
For education only, not medical advice. Reviewed by a Consultant Neurologist and Neuro‑Otologist.