http://www.dizziness-and-balance.com...entral/pvm.htm
If that helps?
I had two LPs, the first neuro screwed up the first one, the second was negative for everything. I was offered a 3rd by the MS specialist, but after repeat mri's and other testing by him? He gave me a diagnosis of PPMS, and said that even if the 3rd LP would have been negative again? He wouldn't change his DX, there was enough other evidence for it, so I passed on LP #3.
I felt my symptoms were consistent with PPMS and so did he.