Comparison of Disease Activity in SPMS and PPMS in the Context of Multicenter Clinical Trials Orbach, Rotem ; Zhao, Zhenming ; Wang, Yong-Cheng ; O'Neill, Gilmore ; Cadavid, Diego Abstract Publication: PLoS ONE Pub Date: October 2012 DOI: 10.1371/journal.pone.0045409 Bibcode: 2012PLoSO...745409O