A One Year Follow-Up Of JCV Serology With Index Values In A French Natalizumab Treated Multiple Sclerosis Cohort (P4.140)

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Objective: To describe JCV serology and one year index follow-up in a natalizumab treated patients cohort. Background: Natalizumab associated PML risk can be stratified according to 3 already known risk factors (natalizumab exposure duration >24months, past history of immunosuppressive drug and positive JCV serology). According to recent studies, index value of JCV serology might be a new potential risk factor enabling us to better stratify the risk of PML occurence during natalizumab therapy. Methods: We prospectively recruited and followed-up all patients treated with natalizumab for their relapsing-remitting multiple sclerosis in our 8 centers. All patients were tested with Gen2 ELISA test in May 2012 and May 2013. In one center, patients were tested every 6 months. Results: JCV seropositivity rate in May 2013 was 56.63% (111/196). Among the entire cohort, 8 patients had the 3 PML risk factors and among them 4 patients had index value >2.5. None of them developped PML. Thirty two patients presented high index value >2.5 in May 2013. One patient developped a PML in October 2013 (5 years of treatment) which was diagnosed at pre-clinical stage. She had high index value during all the follow-up (2.344, 2.823) but no increase of index value at the time of PML diagnosis was observed (2.488). Mean index values was in May 2012 and May, 2013 1.09 ± 1.08 and 1.10 ± 1.04 respectively. Conclusion: High index value might be a new factor in natalizumab associated PML risk stratification but to stop natalizumab to all patients with high index value and who will probably not develop PML, has not to be systematically recommended but to be discussed case by case because of the risk of disease reactivation. Indeed increasing index value before PML diagnosis seems not to be observed in our case.

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