I can't believe that the doctors didn't do a lumbar MRI first!!! Why a spinal tap? That doesn't even sound reasonable! I would think that the lumbar MRI would have been first in their minds, but who knows what goes thru their heads.
And PLEASE -- since you dont' know what the problem is DON'T GO TO THE CHIROPRACTOR!!! Any manipulation at this point could put you in a wheel chair. Two different neurosurgeons told me that any spinal patient needs to steer clear of Chiros' unless they want to end up paralyzed, and especially if you don't have a diagnosis!
I hope your neuro can convince the insurance company that this MRI is needed for a proper diagnosis! And please let us know what the report says once you have it. We can help decipher it when you get it. Best of luck & God bless. Hugs, Lee