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The “Reversal Nystagmus” in BPPV
Benign paroxysmal positional vertigo (BPPV) is the most common type of vertigo encountered in the adult-dizziness clinic. The problem occurs when otoliths that normally reside on the otolith membrane migrate into the semicircular canal system and become canaliths.
When moving around, the patient may, by chance, place their head in a position that causes the aggregated crystals to “sink,” creating a hydromechanical force that, for approximately 85 percent of us, results in a BPPV affecting the posterior semicircular canal. The fluid pressure pushes the posterior semicircular canal (PSCC) cupula, which activates the ipsilateral posterior canal. This results in intense vertigo that is short in duration and disappears in one or two minutes.
Accompanying the vertigo is a repetitive biphasic eye movement called “nystagmus,” the characteristics of which tell the examiner which ear on which side is responsible for the vertigo. This is such a common experience that it is likely that most of us will encounter it sometime during our lives.
The test for the identification of BPPV affecting the posterior canal is called the Dix-Hallpike maneuver. To perform this test, the patient is taken rapidly from the sitting position on the suspect side to the supine position, with the head turned to the right or left and with the head hyperextended. This position is held for 30 to 35 seconds, at which time the patient is brought back up to a sitting position.
These maneuvers are conducted with the patient wearing infrared goggles. When the patient is ready to proceed, the same maneuver is conducted again, this time on the opposite side.
If there is otolithic debris in the posterior canal of the dependent ear, the maneuver will provoke, with a latent period, an intense but short-lasting vertigo and nystagmus that is horizontal rotary with an up-beating vertical component. When the patient is brought back to the sitting position, it is common for the response to reverse direction. That is, the nystagmus, on returning to sitting, is primarily horizontal rotary with a down-beating vertical component.
The paper by Walter and colleagues in this issue of JAAA examines how often the nystagmus reversal occurs. The investigators found that the reversal nystagmus occurred 77 percent of the time. In 19 instances, there was no benign paroxysmal positional nystagmus (BPPN) and the reversal nystagmus occurred 58 percent of the time.
We hope you enjoy reading this interesting report.
19 April 2021 (online)
© 2021. American Academy of Audiology. This article is published by Thieme.
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