The infusion of 300 mg of natalizumab every 4 weeks is an effective therapy for reducing disease activity in relapsing-remitting multiple sclerosis (MS).1,2 Its use is limited, however, by the risk of progressive multifocal leukoencephalopathy (PML), which increases after 2 years of therapy in JC virus (JCV) antibody–positive patients3: the incidence of PML in these patients is between 1/85 and 1/454, with the higher frequency in those with previous use of immunosuppressant drugs.4 Therefore, discontinuation of natalizumab therapy after the second year is recommended to minimize the risk of PML, particularly in JCV antibody–positive patients. The prevalence of JCV antibodies in patients with MS who start natalizumab therapy is high (around 54%5), making discontinuation of therapy a relevant issue for a large number of patients.
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