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The Toronto Observational Study of Natalizumab in Multiple Sclerosis

Background: Natalizumab is indicated for the treatment of relapsing multiple sclerosis (MS) with insufficient response to first-line disease-modifying therapy (DMT). We studied the efficacy of natalizumab for treatment of MS in a single centre observational design. Methods: A retrospective observational study of 146 patients [66% female; mean age 37.4; 72% relapsing remitting MS (RRMS), 28% secondary progressive MS (SPMS)] referred for natalizumab treatment at St. Michael's Hospital MS Clinic between 2007 and August 2009. Data included demographic, clinical (Expanded Disability Status Scale (EDSS) and annualized relapse rate (ARR)) and patient self-report measures. Results: The mean duration of treatment was 20 months in those treated with natalizumab and 97% had received prior DMTs. Eighty-three patients (57%) received at least 12 months of natalizumab treatment. In those who received at least 12 months of treatment, baseline ARR and EDSS were 1.6 and 2.7 in RRMS patients versus 1.0 and 5.4 in SPMS with relapses. The ARR decreased with natalizumab treatment to 0.38 (76% reduction, p<0.001) in RRMS versus 0.32 in SPMS patients (68% reduction, p=0.01). There was a treatment associated 11% reduction in EDSS to 2.4 (p=0.04) in RRMS, but no significant change in SPMS. Eighty-five percent of patients reported improved overall quality of life (QOL) and 62% indicated improved energy. Conclusions: There was a major reduction in relapse rate, stabilization in EDSS and improvement in QOL and energy in some patients on natalizumab, all similar to treatment effects in the pivotal trial.