Detection of JC virus archetype in cerebrospinal fluid in a MS patient with dimethylfumarate treatment without lymphopenia or signs of PML

We report a 76-year-old MS patient, treated with DMF for 3 years. Lymphocytes never showed values below 1240/mu l. CSF analysis revealed 1,988,880 copies/ml of JCV-DNA, JCV-DNA was detectable in serum and anti-JCV-antibody in CSF and serum were highly positive. StratifyA (R)-JCV-test was positive. CD8-positive T-lymphocytes were reduced. Therapy with mefloquine, mirtazapine and cidofovir resulted in complete elimination of the virus in serum and 90% reduction of viral load in CSF. This case shows that despite careful monitoring for lymphopenia JCV spreading to the CSF may occur during treatment with DMF.