My neuro insists that all of his patients on Tysabri undergo a spinal fluid analysis every six months, in an attempt to detect activated JC virus.

He's pulled a number of patients off of the drug who have come up positive for the activated virus but had not yet developed PML.

I'm on Rituxan, another drug associated with PML. I should be scheduled to have a spinal tap for spinal fluid analysis purposes sometime in the next few weeks...