Atypical BPPV is one of the types being sometimes called ageotropic or apogeotropic posterior canal BPPV.
This is a confusing type of BPPV because the otoliths are located in the non-ampullary side of the posterior canal. This creates an opposite nystagmus than that which is seen in a more typical posterior canal BPPV, where the otoliths are located closer to the ampulla due to gravity in normal upright head positions. It is unusual for the otoliths to become stuck in the non-ambulatory side or the short arm of the posterior canal, but it does happen. Depending on the behavior of the otoliths and different head positions and how it deflects the cupula, this can result in positional vertigo and nystagmus that can be down beating and (and may have a) rotary (component) away from the affected ear. The nystagmus direction makes sense if you are familiar with typical posterior canal BPPV causing upbeating, rotary nystagmus towards the affected ear.
The difference in direction is due to how the otoliths are moving in the canal, causing endolymph to move and deflect the cupula in opposite directions.
You will also hear this called non-ampullary or short arm posterior canal BPPV, which is a little more descriptive terminology. Because of the strange direction of the nystagmus, non-ampullary posterior canal BPPV is easily confused with anterior canal BPPV or opposite side BPPV. There are some distinguishing characteristics, so please refer to the free download that provides key differences.
Bridgett Wallace will be discussing atypical BPPV in a more detail on day two of the Virtual Vestibular Summit on April 28, followed by assessment and treatment demonstrations by me. So check out 360neurohealth.com for more information and click here to sign up. Hope to “see” you there!