149. Long-term Disease Activity and Disability Progression of Relapsing-Remitting Multiple Sclerosis in patients with Natalizumab: A Single-Centre Retrospective Observational Study

Natalizumab is one of the first high-efficacy treatments approved for relapsing-remitting multiple sclerosis (RRMS). There are limited data on Its efficacy has beyond 5 years of prescription on disease activity and disability progression. We conducted a retrospective observational single-center study in Neurology department of National Institute Mongi Ben Hmida of Neurology, Tunis, Tunisia. We included RRMS patients diagnosed using McDonald 2017 criteria and treated with Natalizumab during over five years. Annualized relapse rate (ARR) was calculated. No evidence of disease activity (NEDA) was defined by absence of relapses, stability of expanded disability status scale (EDSS) and absence of radiological activity. EDSS was assessed at natalizumab initiation and yearly after. EDSS improvement was defined by persistant reduction of at least 1 point over 6months. Its worsening was defined by a persistant increase of at least 1 point over 6months. Its stability was defined by absence of variation or a reversible variation over six months. Cerebral MRI was performed yearly. Absence of radiological activity was defined by absence of new or enlarging T2/FLAIR lesions and/or contrast enhancing lesions after natalizumab initiation. Among 134 patients treated with natalizumab, we included 36 patients. Sex-ratio was 0.2. Median age at disease onset was 17.5 years (IQR=7). Five case of pediatric onset RRMS were noted (13.9%). Highly active RRMS accounted for 52.8% (n=19). Median EDSS at RRMS diagnosis was 2 (IQR=2). All patients received natalizumab as a second-line therapy after interferons. Median time to escalation was 4.5 years (IQR=9). Median EDSS at escalation was 3.3 (IQR=3.9). median duration of natalizumab prescription was 8 years. A sustained absence of relapse was achieved beyond five years in 61.1% of patients (n=22). Sustained EDSS stability during follow-up was obtained in 63.9% of patients (n=23). Absence of radiological activity was observed and maintained during follow-up in 75% of patients (n=27). NEDA was present consistently in 61.1% of patients (n=22). Our study showed that Natalizumab is a treatment with sustained long-term efficacy. These results are to be confirmed by larger-scale prospective studies.