The primary aim of this study is to evaluate the effect of using Tysabri on changes in the brain using MRI and on disease progression in patients with relapsing-remitting Multiple Sclerosis over 5 years.

This is a prospective, observational, single-blinded, longitudinal study of natalizumab effect on brain atrophy development and disability progression in multiple sclerosis patients over 5 years, which will evaluate originally treated patients with natalizumab who participated in a prospective 1- and 2-year VWMTR study. (Zivadinov et al., 2011b) All subjects will be assessed at 5-year follow-up with the same clinical examinations and will obtain 1.5T MRI examination on the same scanner that did not undergo any upgrade changes in the period of 5 years.

Inclusion Criteria:

• Participation in natalizumab 1-year follow-up study
• Participants were aged 18-65
• Have clinically definite MS according to the Polman criteria of either RR or RSP disease type
• EDSS scores ≤6.5
• disease duration <30 years
• normal kidney function (creatinine clearance >59 mL/min)
• started therapy either with natalizumab or IM interferon beta-1a (IFNβ-1a)
• Signed informed consent
• Normal kidney functioning (creatinine clearance >59)
• None of the exclusion criteria

Exclusion Criteria:

• A clinically significant infectious illness (e.g., cellulitis, abscess, pneumonia, septicemia) within 30 days prior to 5-year follow-up visit
• Nursing mothers or pregnant women who will need to undergo 5-year follow-up MRI
• Unwillingness or inability to comply with the requirements of this protocol including the presence of any condition (physical, mental, or social) that is likely to affect the subject's ability to comply with the study protocol
• Any other reasons that, in the opinion of the Investigator, indicate that the subject is unsuitable for enrollment into this study

Multiple Sclerosis - relapsing remitting