BPPV: why displaced crystals cause positional vertigo
BPPV (benign paroxysmal positional vertigo) causes short bursts of false spinning set off by head position, from loose crystals in a fluid-filled semicircular canal.
Remember
Loose crystals in a semicircular canal move with gravity and give a false signal of head rotation, which is why BPPV causes brief positional vertigo with normal hearing.
Memory aid
rocks in the wrong room
The crystals belong in the utricle but have wandered into a canal.
Benign paroxysmal positional vertigo (BPPV) is a mechanical problem, and the cause is loose crystals rather than inflammation. Benign means it is not dangerous in itself. Paroxysmal means the attacks come in sudden short bursts. Positional means a change of head position sets one off.
The inner ear holds tiny calcium carbonate crystals called otoconia. They normally sit in the utricle, a small sac that helps sense gravity and straight-line movement. If some come loose, they can enter a semicircular canal, one of the three fluid-filled loops that sense head rotation. The posterior canal is the one most often affected.
Once crystals are in the canal, a change in head position moves them under gravity and disturbs the endolymph, the fluid inside the canal. The hair cells in that canal (the sensory cells that detect fluid movement) then report rotation that is not happening, so the brain feels vertigo, a false sensation of spinning. The vertigo fades as the crystals settle, which is why attacks are brief.
Hearing stays normal because the cochlea, the hearing part of the inner ear, is not involved. So there is no hearing loss and no tinnitus (ringing in the ears). That is the clue that separates BPPV from conditions such as Ménière disease, whose mechanism is excess endolymph distending the inner-ear ducts.
Key facts
- Cause
- Loose otoconia move out of the utricle into a semicircular canal, most often the posterior one.
- Pattern
- Attacks are brief, lasting seconds and under about 2 minutes, and are set off by head movements such as rolling over in bed or looking up.
- Hearing
- Hearing stays normal and tinnitus is absent, so hearing loss or tinnitus suggests another cause.
- Test
- The Dix-Hallpike manoeuvre, a bedside test, provokes vertigo and nystagmus (involuntary jerking eye movements).
- Treatment
- The Epley manoeuvre moves the head through a series of positions that guide the crystals out of the canal.
Exam traps
- Excess endolymph in the inner-ear ducts is the mechanism of Ménière disease, not BPPV. Its vertigo attacks last from about 20 minutes to 12 hours and come with hearing loss and tinnitus, unlike brief positional spells with normal hearing.
- Vestibular neuritis (inflammation of the balance nerve, thought to be viral) spares hearing, as BPPV does, so normal hearing does not separate them. It gives a single sustained attack of severe vertigo lasting days, not repeated brief spells set off by rolling over or looking up.
- Cochlear hair cells detect sound, not head position. Their gradual loss causes progressive hearing loss rather than episodes of vertigo, so they do not explain a brief positional spell with normal hearing.
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