Study design and participants
multiple sclerosis, RRMS
VIRUS, MULTIPLE SCLEROSIS, PML
This observational study included patients admitted to the MS unit of a tertiary referral hospital (Bellvitge University Hospital, Barcelona, Spain). Patients diagnosed with relapsing–remitting multiple sclerosis (RRMS) according to the McDonald criteria [The PML risk stratification moment (STRm) was established for the first time when JC virus antibody levels were assessed between January 2018 and March 2021. Patients were classified according to their treatment after STRm into continued NTZ (in case of JCV negativity) or changed to OCR (in case of JCV positivity) after a minimum of two months of planned washout. The treatment depended on the JC virus status at the discretion of the attending physicians and under expert committee approval. JCV positivity was considered when a minimum titer of 0.4 was obtained.The patients received intravenous NTZ every 4 weeks and intravenous OCR every 6 months. During washout periods, all patients who changed NTZ received monthly doses of one gram of intravenous methylprednisolone.