The neurologist is going to do a lumbar puncture on my daughter.  What
are the chances that this will show anything?  Will the fact that she is
on abx make any difference?

From Dr. Burrascano's Guidelines:

         Antigen detection tests including PCR are now available, and
although they are very specific, sensitivity remains poor, possibly less
than 30%.  This is because Bb causes a deep tissue infection and is only
transiently found in body humors. Therefore, multiple specimens must be
collected to increase yield, and a negative result does not rule out
infection, yet a positive one is significant. The patient must be antibiotic
free for at least six weeks before testing. Antigen capture can be done on
urine, CSF, and synovial fluid. PCR can be done on {*filter*} (buffy coat is
best), urine, CSF, any other body fluid including {*filter*} milk, and on tissue
biopsy specimens.

Spinal taps are not routinely recommended, as a negative tap does not rule
out Lyme. Antibodies to Bb can be detected in the CSF in just 20% of
patients with late disease. Therefore, spinal taps are only performed on
patients with pronounced neurological manifestations, if they are
seronegative, or are still significantly symptomatic after completion of
treatment. When done, the goal is to rule out other conditions, and to
determine if Bb antigens are present. It is especially important to look for
elevated protein and mononuclear cells, which would dictate the need for
more aggressive therapy, as well as the opening pressure, which can be
elevated and add to headaches, especially in children.

I ahve had quite a few of these. Myself I've gotten good results and I think it
was the best test for diagnosing me with Lyme Disease. It does seem to be the
best in diagnosing diseases. Goo luck to you and your daughter. If you would