It is difficult to differentiate between PML and an MS flare up. You need to be seen by a neurologist who is familiar with PML or at least who will communicate with one who is. You can find names of PML-experienced doctors via the following link to the June 2013 New York Academy of Sciences PML presentation here http://www.nyas.org/Events/Detail.aspx? ... 14f04bf58d
The earlier the treatment of PML, the better are the odds of successful treatment. If you get a spinal tap, make sure the doctor and lab understand that you need a quantatative analysis of the JCVirus in the fluid, not just a test that tell whether you are positive or not. This can only be done only at a few labs in the US. One is focus Labs in California. You don't want to have to do this again to get the viral load, so be sure you don't get a report that is only "detected or not detected" . The quanitative analysis (which is a viral load count) will tell you where you are, as you fight the virus. It only takes 24-48 hours to get a report back
If JCV is present in the CSF, then they will generally start the PLEX. Then the debate is a little bit of IRIS may be desirable. If one has PML, from tysabri then treatment with steroids may lower the immune system and allow the JCVirus to get worse. It is a double edged sword. And for this reason it may not be desirable to treat immediately with steroids,or even soon after until IRIS is actually present. This all has to be determined by a good neurologist who understands what your MRI shows.
The main point here is, if a PML competent neurologist recomends it, to do a spinal tap as soon as possible when there are symptoms and especially more than one symptom such as change in speech, handwriting, gait etc and JCV positive. Also, PML can present itself without enhancement on the MRI. There are a number of doctors around the country who are experts in PML and many who have never treated. What area are you in?