Does Long-Term Natalizumab (NTZ) Therapy Normalize Brain Atrophy Rates and Quality of Life (QOL) in Relapsing Remitting Multiple Sclerosis (RRMS)?

Primary Aims: To determine how effective long term Natalizumab (NTZ) therapy is in slowing the progression of whole brain atrophy. Whole brain atrophy rates will be measured through magnetic resonance imaging (MRI) scans and compared between patients with Multiple Sclerosis (MS) who have been using NTZ for at least 2 years versus age and gender-matched healthy controls. The primary outcome will be whole brain atrophy rate measured as the percent change in brain volume (PBVC) over a two-year period. Primary hypothesis: The investigators hypothesize that long term (\>2 years) NTZ therapy will slow the rate of whole brain atrophy in patients with Multiple Sclerosis (MS) (as measured by percent change in brain volume), reaching a whole brain atrophy rate similar to that of non-MS controls (a true "disease activity free" state).