Natalizumab induces a rapid improvement of disability status and ambulation after failure of previous therapy in relapsing‐remitting multiple sclerosis

Background: Natalizumab (Tysabri) is a monoclonal antibody that was recently approved for the treatment of relapsing‐remitting multiple sclerosis (RRMS). Our primary objective was to analyse the efficacy of natalizumab on disability status and ambulation after switching patients with RRMS from other disease‐modifying treatments (DMTs). Methods: A retrospective, observational study was carried out. All patients (n = 45) initiated natalizumab after experiencing at least 1 relapse in the previous year under interferon‐beta (IFNB) or glatiramer acetate (GA) treatments. The patients also had at least 1 gadolinium‐enhancing (Gd+) lesion on their baseline brain MRI. Expanded Disability Status Scale (EDSS) scores, and performance on the Timed 25‐Foot Walk Test and on the Timed 100‐Metre Walk Test were prospectively collected every 4 weeks during 44 weeks of natalizumab treatment. Brain MRI scans were performed after 20 and 44 weeks of treatment. Results: Sixty‐two per cent of patients showed no clinical and no radiological signs of disease activity, and 29% showed a rapid and confirmed EDSS improvement over 44 weeks of natalizumab therapy. Patients with improvement on the EDSS showed similar levels of baseline EDSS and active T1 lesions, but had a significantly higher number of relapses, and 92% of them had experienced relapse‐mediated sustained EDSS worsening in the previous year. A clinically meaningful improvement in ambulation speed was observed in approximately 30% of patients. Conclusions: These results indicate that natalizumab silences disease activity and rapidly improves disability status and walking performance, possibly through delayed relapse recovery in patients with RRMS who had shown a high level of disease activity under other DMTs.