There have now been 4 cases of PML in patients on tecfidera for MS. I don't have complete details on all the cases. I
do know that the first case reported had a very low white blood cell count for years before developing PML. One of the
recent cases had a normal white cell count at all the screening tests before they developed PML. I don't have details
on the other cases.
PML is a brain infection caused by the JC virus. This virus infects over
half of people, and stays in the body lifelong after infection. The JC virus is normally harmless, but in people that
are immunosuppressed, it can cause PML. PML has been a significant issue in MS patients treated with Tysabri, and there
have also been rare cases of PML with Gilenya.
When Tecfidera first came on the market, there had been 4
cases of PML reported in people with psoriasis treated with a similar drug. So the possibility of PML has been
a concern. But the previous cases were all in people who had been treated with other drugs that strongly suppress the
I have a number of patients on Tecfidera, but I would not recommend changing treatment for
now. I am carefully following white cell counts and also the total lymphocyte count. I have switched treatment
in a few people with a persistently low count.
This looks like a rare problem, but not completely avoidable.
I will continue to check white cell and lymphocyte counts in the blood at every visit for my patients on tecfidera,
and will keep discussing the risks at each clinic visit.