THURSDAY, Aug. 2 (HealthDay News) -- Early treatment with the drug interferon slows the progression of multiple sclerosis (MS) in people with the first symptoms of the disease and reduces impairment, an international study shows.

The study of 468 people found that 37 percent of those who got every-other-day injections of interferon beta-1b progressed to full-blown MS over three years, compared to 51 percent of those who got inactive injections, according to the report in the Aug. 4 issue of The Lancet.

Interferon treatment also reduced the progression of disability by 40 percent, the report said.

Those numbers should help resolve a running debate about interferon treatment for people who experience a first episode of disability that warns of MS, said Dr. Ludwig Kappos, head of the MS-Research Group at University Hospital in Basel.

"Other studies, including the early part of this one, showed that early treatment can delay occurrence of a second episode that allows one to make the diagnosis of multiple sclerosis," Kappos said. "But that the treatment had an impact on remaining ability was not clear. This study shows there is a difference, at least for some people."

MS is a disorder of the central system in which the fatty tissue called myelin that surrounds nerve cells is destroyed. It is thought to be an autoimmune condition, wherein the body attacks its own tissue. Several laboratory-made versions of interferon are commonly used to treat the disease.

To Patricia O'Looney, vice president for biomedical research at the National Multiple Sclerosis Society in New York City, an important aspect of this study is that it measured the progression of the disease precisely, patient by patient, using the well-established expanded disability status scale (EDDS). That scale goes in half-point steps from 0.5, the first sign of the disease, to 9.5, total disability.

"What makes this study different is that it shows delay in progression on the EDDS scale, which other studies have not done," O'Looney said.

The results "provide more evidence to support the value of early treatment," she said. "There has been disagreement about whether early treatment is beneficial. This provides additional evidence that early treatment delays progression on a disability scale."

An accompanying editorial by Dr. Sean Pittock, a neurologist at the Mayo Clinic, praised the study, saying, "Kappos and colleagues have set a new standard against which future extension trials will be compared."

But Pittock said the results of the trial should be "interpreted with care, because the magnitude of benefit, although significant, is clinically small. This follow-up should not be misconstrued as evidence for a 'treat all' approach."

Kappos said he agreed with that assessment, but he noted that the trial covered only the first few years of a condition that could progress for decades. "In the early stages of the disease, the changes are minor," he said. "Later on, they can cause more severe problems. Changes that may look minor at an early stage take on greater importance."

"Even if it is only marginal, a significant delay is still a delay," O'Looney said. "To someone with MS, even a marginal delay in the loss of the ability to walk is important."

What the study results provide in the decision about treatment of a specific patient is "one more argument why it is important to have this treatment," Kappos said. "Then it is their decision. The treatment can cause side effects, and they have to weigh one against the other."

But the side effects of interferon treatment generally are "benign," Kappos added. The treatment would be especially helpful to patients in whom silent brain lesions are found by MRI scans, he said.

"This is an important argument to be considered by patients," Kappos said, and the trial results have changed the frame of that discussion. "Several years ago, neurologists hesitated to discuss it," he said, referring to early treatment. "Now, they can take the time to discuss it."

SOURCES: Ludwig Kappos, M.D., head, MS-Research Group, University Hospital, Basel, Switzerland; Patricia O'Looney, Ph.D., vice president, biomedical research, National Multiple Sclerosis Society, New York City; Aug. 4, 2007, The Lancet

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