RESUMEN
BACKGROUND: Progressive multifocal leukoencephalopathy, caused by oligodendrocyte lytic infection by JCVirus, is a growing concern for patients undergoing immune modulatory therapies for treatment of autoimmune diseases, such as multiple sclerosis (MS). The objective of JEMS was to describe the prevalence of anti-JCV antibodies in MS patients and to assess the various factors associated to it. METHODS: Serum samples were collected and tested for anti-JCV antibody using the STRATIFY JCV™ assay in 131 Portuguese MS patients. Factors potentially associated with prevalence were also evaluated, as well as the effect of established risk factors. RESULTS: In the population of 131 Portuguese patients included in the JEMS, the overall anti-JCV antibody prevalence was 69.5% (95% CI, 61.6-77.4). The anti-JCV antibody prevalence did not seem to be influenced by demographic characteristics, although results demonstrate a non-significant trend for increased prevalence with age. Disease characteristics, treatment duration, treatment history, prior immunosuppressive therapy use and natalizumab exposure duration did not seem to be associated with anti-JCV prevalence. CONCLUSION: The results of Portuguese MS patients participating in the JEMS study present some differences when compared with the global population and literature results. An overall prevalence higher than expected raises awareness for data confirmation with greater sample size studies.