How did I suddenly go from JCV- to JCV+?

Here is My Question:
I was JCV- in June 2014, Dec 2014, and in March 2015. Somehow in early July 2015, I am suddenly HIGHLY JCV+ over 2.0.

Can you help me understand how that happened. I know JCV is a bit of an unknown, but what the heck? I had no major changes over those months, no sickness, no new medicines, no travel, no new pets exposure.

Also, I'm on Tecfidera & soon to transition to Gileyna. I see both Tecfidera (w/ a PML warning) and Gilenya (w/o a PML warning) have at least 2 cases each of associated PML. Is it smart to make the switch at all given my JC status?

Thanks

Answer:
The John Cunningham Virus, abbreviated JC virus, causes no symptoms or illness at the time of exposure in most people. That said, there is also no evidence that a sudden increase in JC virus antibody levels has anything to do with recent exposure to the virus. Many people, if not most, who are JC virus antibody negative have already been exposed to the virus. The virus periodically replicates inside us and this process may lead to an increase in JC virus antibody levels .

The most important piece of information in your message is the fact that you are not even taking Tysabri. JC virus antibody levels are ONLY used to assess your risk of PML while receiving Tysabri. The rate of PML is far too low in either Tecfidera or Gilenya treated patients to make this a useful test in patients on these treatments. In the case of Tecfidera it is far more important to monitor lymphocyte counts.

A little math will help you understand: We know that the overall risk of PML in all Tysabri treated patients is 1 in 1000. If you are JC Virus antibody negative your maximal risk of PML is 1 in 10,000 and if you are JC virus antibody positive that risk is 1 in 100 after 2 years of therapy (approximately a 100 fold difference since approximately 50 % of patients are JCV antibody positive).  If JC virus antibody titers are predictive of the risk of PML in MS patients on other treatments and this relative risk increase is the same for other treatments (BOTH TOTALLY UNKNOWN BUT ASSUMPTIONS FOR THIS EXERCISE IN MATH), then the utility of this test will depend on the overall risk of PML in a person receiving treatment with either Tecfidera or Gilenya. At present there is no evidence that the risk of PML on either drug is more than 1 in 25,000. (compared to 1 in 1000 on Tysabri). Therefore, if (and again this is an unknown)  high JCV antibody levels increase the risk of PML to a similar extent in people on Tecfidera or Gilenya, then your highest risk for PML would be 1 in 2,500 (25,000 divided by 10). In all likelihood these numbers overestimate the risk.  A risk less than 1 in 2500 is not useful for making decisions unless your Lymphocyte counts drops too low.

Revere (Rip) Kinkel MD
Director of the Multiple Sclerosis Program
Professor of Clinical Neurosciences
University of California San Diego