according to the NY Times.

http://www.nytimes.com/2012/07/18/he...fVCA1E7drZJjNQ

The most widely prescribed drug for treating multiple sclerosis has little or no effect on a patient’s progression to disability, a new study has found.

The medicine, interferon beta, does help reduce the development of brain lesions and limit the frequency of relapses, but until now there have been few well-controlled long-term studies demonstrating its effectiveness at preventing the onset of irreversible disability.

Researchers at the University of British Columbia prospectively collected data on 868 M.S. patients treated with interferon beta, comparing them with 1,788 patients who never took the drug. Using a well-validated scale, they found that those who took interferon beta were no less likely to suffer long-term disability than those who took none.

Interferon beta drugs are commonly used to treat relapsing-remitting M.S., the most common form of the disease. M.S. is an autoimmune disease that damages the myelin sheath surrounding the nerve cells. Its course varies widely, but it is usually a relapsing illness that produces a variety of symptoms, including muscle spasms and difficulty walking, bladder and bowel problems, vision and hearing disturbances, speech problems, difficulties with reasoning and attention span and more.

The disorder is chronic and incurable, and its outcome is variable and hard to predict. But life expectancy can be normal, and many people live with the disease for decades, still able to walk and work with minimal disability.

The senior author, Helen Tremlett, an associate professor of neurology at the University of British Columbia, cautioned that the study, published online on Tuesday in the Journal of the American Medical Association, does not show that interferon beta is useless.

“These drugs were licensed because they reduce relapse and have a better outcome with lesions,” she said. “That has not changed.”

Other experts found the study discouraging. “It’s an interesting paper and an important paper,” said Dr. David A. Hafler, chairman of the neurology department at Yale. “If interferon does have an effect on disability, then it’s a relatively small effect.”

Dr. Claire Riley, director of the Multiple Sclerosis Clinical Care & Research Center at Columbia University, was equally impressed with the work and somewhat troubled by its results. “It’s a little dispiriting to see this well-designed, well-conducted assessment showing no association between reduction of disability progression and interferon use,” she said. “But the key is that all M.S. is not created equal, and we now have eight approved drugs in four different classes that allow us to better react to patients who are not having a response to therapy.”

Previous studies have found that interferon beta does prevent disability, but the authors point out that many of them were marred by methodological problems — the use of control groups too ill to start medication, for example — that this study avoided.

At the same time, they acknowledge certain weaknesses of their own study, in particular the problem that people who take no medicine are also likely to be among those who are the least ill and therefore least likely to become disabled in any case.

But after controlling for sex, age at onset, disease duration, relapse rate and other factors, they could find no association between taking interferon beta and any reduction in progression to disability. Relapses and brain lesions do not, apparently, drive disability, Dr. Tremlett said.

“There may be other processes at work,” she added. “In an ideal world, we want drugs that target whatever is driving long-term disability. We need other drugs aiming at other targets in the brain.”

A version of this article appeared in print on July 18, 2012, on page A14 of the New York edition with the headline: Multiple Sclerosis Drug Doesn’t Prevent Onset of Disability, Study Finds.