Therapeutic decision-making for relapsing MS. Options are shown for different clinical scenarios and based on JCV status. Active MS is defined by clinical relapses or the development of new focal MRI white matter lesions. Treatment options can also include trials of different preparations of interferon β (IFN-β), particularly advancing from once-weekly (Avonex) to a more frequent (e.g., Rebif, Betaseron/Extavia) dosing regimen, as well as use of natalizumab in JC virus-positive pts.