Stan,
 
I concur with Dr. Tim Vollmer's comments about Gilenya.

With tens of thousands of patients safely and effectively on Gilenya, the very low risk of PML seems appears linked to prior treatment with other strong immunosuppressive drugs.

There may need to be some greater caution in using Gilenya on top of similar agents where the total numbers of lymphocytes are dramatically lowered, perhaps separating them further in time, and also testing to see if the patient carries the JC virus that causes PML to see if they are at risk  in those circumstances.

As Dr. Vollmer indicates, medical guidelines for these uncommon
cases will probably be established in the near future.

Brian R. Apatoff, MD, PhD

Multiple Sclerosis Institute
Center for Neurological Disorders

Associate Professor Neurology and Neuroscience,
Weill Medical College of Cornell University
Clinical Attending in Neurology, New York-Presbyterian Hospital