The pathogenesis of MS remain elusive, however some studies have linked the disease with infection by Epstein-Barr virus; therefore the use of drugs with immunosuppressive or immunomodulating action alone may be less suitable for primary progressive MS.This study will evaluate treatment with hydroxyurea (HU) in primary progressive MS. Hydroxyurea act by inhibiting the synthesis of deoxynucleotides essential for viral transcription,HU has recently been used in combination with antiretroviral drugs in HIV and has been shown to limit immune activation and suppress viral load by both antiviral and cytostatic activities. Furthermore has been demonstrated experimentally that HU suppressed the expression of EBV. For these reasons HU could be useful in primary progressive MS with cytostatic and antiviral action , confirming the role of EBV in the pathogenesis of MS.