Since PML is associated not only to MS but other rare disorders, I decided to post this. I hope someone will find it to be helpful. I look forward to any and all comments.
The only reason that PML is associated with MS is from a patient's use of the drug Tysabri. To date, 285 MS patients have contracted PML. Prior to starting on Tysabri, patients are usually tested to see if they have the JC virus in their system. If positive, the patient then has to decide if he/she wants to risk taking the drug or not. Under certain conditions, the risk factor can be 1:500.