Effect of natalizumab on clinical and radiological disease activity in multiple sclerosis: a retrospective analysis of the Natalizumab Safety and Efficacy in Relapsing-Remitting Multiple Sclerosis (AFFIRM) study

Background: The efficacy of natalizumab on clinical and radiological measures in the phase III Natalizumab Safety and Efficacy in Relapsing-Remitting Multiple Sclerosis (AFFIRM) study has prompted the investigation of whether natalizumab can increase the proportion of patients with relapsing-remitting multiple sclerosis who do not have disease activity. Methods: Post-hoc analyses of data from the AFFIRM study were done to determine the effects of natalizumab compared with placebo on the proportion of patients who were free of disease activity over 2 years. Absence of disease activity was defined as no activity on clinical measures (no relapses and no sustained disability progression), radiological measures (no gadolinium-enhancing lesions and no new or enlarging T2-hyperintense lesions on cranial MRI), or a composite of the two. Findings: 383 (64%) of 596 patients taking natalizumab and 117 (39%) of 301 taking placebo were free of clinical disease activity (absolute difference 25·4%, 95% CI 18·7-32·1%, p<0·0001); 342 (58%) of 593 and 42 (14%) of 296 were free of radiological disease activity (43·5%, 37·9-49·1%, p<0·0001); and 220 (37%) of 600 and 22 (7%) of 304 were free of combined activity (29·5%, 24·7-34·3%, p<0·0001) over 2 years. The effect of natalizumab versus placebo was consistent across subgroups of patients with highly active or non-highly active disease at baseline. Interpretation: Disease remission might become an increasingly attainable goal in multiple sclerosis treatment with the use of newer, more effective therapies. Funding: Biogen Idec.