REPORT FROM THE AMERICAN ACADEMY OF NEUROLOGY (AAN) ANNUAL MEETING, SAN DIEGO, CA, MARCH 16-23, 2013 – Natalizumab is commonly used following first-line treatment failure/intolerance, but switching may be advisable after two years in patients with anti-JC virus antibody positivity. However, switching therapies is challenging in practice due to the risk of increased disease activity upon natalizumab withdrawal.