Question
Is there any clinical significance as to the time of onset of the nystagmus and dizziness when doing the Hallpike for example, 10 seconds versus 40 seconds?Answer
The pattern of nystagmus, including latency, can shed some light on whether the BPPV is cupulolithiasis or canalithiasis. Typically, the nystagmus associated with cupulolithiasis (where the otoconial debris is attached to the cupula) has a shorter latency, but the nystagmus is more persistent and consistent. By that, I mean that the intensity of nystagmus remains steady over a duration usually exceeding thirty seconds. The nystagmus associated with canalithiasis (free floating otoconia) has a latency of several seconds, then the nystagmus build in a crescendo pattern, then gradually abate. Squires et al (2004), through mathematical computation estimate that it takes approximately five seconds for free floating otoconia to settle in a typical semi-circular canal, explaining the latency of response in BPPV. This difference in nystagmus response can influence the choice of treatment. Many specialists use the Semont maneuver if they suspect Cupulolithiasis, but use a modified Epley procedure for canalithiasis.
Squires et al (2004) A mathematical model for top shelf vertigo: the role of sedimenting otoconia in BPPV. J biomech. Aug:37(8):1137-46
Alan Desmond, Au.D is the director of Blue Ridge Hearing and Balance Clinic in Bluefield and Princeton, WV. Thieme Medical Publishers released his book Vestibular Function: Evaluation and Treatment in April 2004. He can be reached at BRHBC@comcast.net