The incidence of persistent antibody positivity associated with natalizumab is 6%. Reduced clinical efficacy is apparent in persistently positive patients. Patients with a suboptimal clinical response or persistent infusion-related adverse events should be considered for antibody testing.

With the advent and widespread use of partially effective disease modifying drug therapies for multiple sderosis (MS), future dinical trials will undoubtedly test experimental interventions against standard therapy, or will test combinations of drugs against standard therapy. In either case, incremental progress in slowing disability progression in future MS dinical trials will require much larger sample sizes, more sensitive outcome measures, or a combination of the two. Because improved dinical outcome methods would likely accelerate progress in MS therapeutics, the National Multiple Sclerosis Society (NMSS) convened an international task force in 1994 to recommend improved clinical outcome measures. As the result of a two-year process of discussion and data analysis, the task force recommended the Multiple Sderosis Functional Composite (MSFC) as a new clinical outcome measure for future MS trials. MSFC consists of timed tests of walking, arm function, and cognitive function, expressed as a single score along a continuous scale. The task force recommended that MSFC be induded in future MS trials, and recommended a series of validation studies. Subsequent studies have provided evidence that MSFC correlates moderately with Expanded Disability Status Scale (EDSS), and that correlation is driven by strong correlations with the ambulatory function component; arm function and cognitive function correlate at lower levels with EDSS. The MSFC correlates better than EDSS with magnetic resonance imaging (MRI) variables, including brain atrophy, and shows significant correlation with patient-reported disease-related quality of life (QOL). MSFC and short-term change in MSFC correlate with future clinical and MRI status, and the strength of the correlations compares favorably with well-known cardiovascular risk factors. The studies in aggregate indicate that MSFC and MSFC change are clinically meaningful, and that MSFC has substantial advantages over alternative clinical outcome measures for MS clinical trials.

Low-contrast letter acuity (L-CLA) scores demonstrate concurrent and predictive validity in patients with relapsing-remitting and secondary progressive multiple sclerosis (MS). L-CLA testing provides additional information relevant to the MS disease process that is not entirely captured by the Multiple Sclerosis Functional Composite.

Natalizumab reduces visual loss in patients with relapsing multiple sclerosis. Low-contrast acuity testing has the capacity to demonstrate treatment effects and is a strong candidate for assessment of visual outcomes in future multiple sclerosis trials.

The primary clinical outcome for the IFN beta-1a clinical trial underestimated clinical benefits of treatment. Results in this report demonstrate that IFN beta-1a treatment is associated with robust, clinically important beneficial effects on disability progression in relapsing MS patients.