In article <4vaamm$ur at sjx-ixn3.ix.netcom.com>, heardoc1 at ix.netcom.co says...
>>I'm interested in finding out if anyone knows what is called true BPPV
>when performing the Dix Hallpike maneuver. I know all the classic signs
>to look for when performing the test (delayed onset, subjective feeling
>of dizziness, etc) but I recently heard that in order for it to be true
>BPPV the nystagmus will change directions when the patient is brought
>to the original sitting position.
There are several articles in the literature about nystagmus reversal
following a positive Hallpike (reversal can sometimes also be seen if you
continue recording caloric responses for 4-5 minutes). This reversal is not
considered a "must-have" for diagnosing BPPV. The important parameters are
delay, ROTARY nystagmus with a crescendo-decrescendo character, symptoms, and
fatiguablitiy with repetition. Since it's ROTARY nystagmus that's important,
you DO NOT need to record Hallpike's! Conventional EOG-electrodes cannot
record torsional eye movements. You need to look at the eyes, with or without
Freznel lenses. Torsional nystagmus is not reduced by fixation, so you only
need Freznel's for magnification, you can do without. Don't worry about the
upward Hallpike, it shouldn't be used to diagnose BPPV since it can be
contaminated by orthostasis.