ScienceDaily (Apr. 19, 2007) — According to a study that appears in the April 17 issue of Neurology, researchers at the University of Pennsylvania School of Medicine have found that natalizumab (TYSABRI®) -- a drug that slows disability and reduces relapse rates in patients with multiple sclerosis (MS) -- also reduces vision loss in patients with relapsing MS. Vision loss is one of the most common and disabling symptoms of MS.

"Not only does natalizumab prevent the worsening of vision loss in people with relapsing MS, but it is also associated with significant reductions in the likelihood of sustained vision loss due to inflammatory demyelination of nerve fibers that connect to the eye, a common cause of visual loss in MS," says Laura J. Balcer, MD, MSCE, Associate Professor of Neurology and Ophthalmology at Penn, and lead author of the paper.

The researchers analyzed data from two randomized, double-blind, placebo-controlled, parallel group, phase 3 clinical trials involving 2,138 men and women with relapsing MS from clinical centers in Europe, North America, Australia, and New Zealand. More than half of the participants received natalizumab every four weeks for two years, while the remaining participants received placebo. Visits were conducted every 12 weeks and visual function testing was performed at each study visit. Low-contrast letter acuity was measured using low-contrast letter charts (eye charts with gray letters on a white background).

Researchers found vision loss -- a worsening of vision defined as a two-line (10-letter) reduction in letter chart scores -- was reduced by as much as 47% among people taking natalizumab, compared to those taking placebo.

"Not only do the findings of the study add to our understanding of the effects of natalizumab, but the results provide strong validation for a simple, sensitive, cost-effective, and clinically meaningful measure of visual function in MS," advises Dr. Nicholas LaRocca, Associate Vice President, Health Care Delivery and Policy Research at the National MS Society.

The researchers caution that, as with any therapy, the benefits of natalizumab must be considered in the context of potential risks or complications. In the case of natalizumab, three confirmed cases of progressive multifocal leukoencephalopathy (PML) -- a rare, often lethal brain disease -- have been reported.

Despite the fact that vision loss is a common and important cause of disability in MS, the natalizumab clinical trials were the first to include a test of visual function. These trials showed that low-contrast letter acuity eye chart testing is an effective measure for assessing visual outcomes, and may be useful in future clinical trials.

This study was supported by Biogen Idec and Elan, makers of natalizumab. Dr. Balcer has received support for consulting from Biogen Idec as well as from other companies for work on developing visual outcome measures for MS clinical trials.

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Adapted from materials provided by University of Pennsylvania School of Medicine, via EurekAlert!, a service of AAAS.

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