At relapse , an increase in EDSS score of 0.5 points occurred in 71 % of natalizumab and 84 % of placebo patients ( P = 0.0088 ) ; an increase of 1.0 point occurred in 49 % of natalizumab and 61 % of placebo patients ( P = 0.0349 ) ( mean increase in EDSS at relapse : natalizumab = 0.77 ; placebo = 1.09 ; P = 0.0044 ) .