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Dr. Paolo Zamboni looks on before speaking about the breakthrough medical research he has done at the Neurologist Seminar in Toronto on April 14, 2010.NATHAN DENETTE

A new study attempting to evaluate the validity of research into the prevalence of blocked veins in multiple sclerosis patients has concluded the evidence is too conflicting and inconsistent to draw any concrete conclusions.

The study, published Monday in the Canadian Medical Association Journal, adds another layer of uncertainty to the controversy surrounding the contentious issue, which has been brewing for about two years following media reports of the possible link between blocked veins and MS.

"I think it's really hard to come to any conclusion, any definitive conclusion," said Andreas Laupacis, lead author of the study and executive director of the Li Ka Shing Knowledge Institute at St. Michael's Hospital in Toronto. "We won't know for a few years the full story."

Italian doctor Paolo Zamboni popularized a theory that blocked or malformed neck veins cause or somehow contribute to MS, and that a relatively minor procedure to open them can treat symptoms.

Clinics around the world, many of them charging high fees, began offering the procedure and patients flocked to them from countries such as Canada, which doesn't cover the treatment due to a lack of solid evidence.

Over the past two years, thousands of patients and advocates have used political rallies and social media campaigns to pressure governments to bring the treatment to Canada. They have had some success, with provinces such as Saskatchewan pledging last week to pay for patients to get the treatment in the U.S. and participate in a study there.

The federal government announced earlier this year it would fund a clinical trial to investigate the vein-widening procedure, referred to by proponents of the theory as "liberation treatment."

But the findings of the new study indicate it's still too early to know whether blocked veins, a condition described by Dr. Zamboni as chronic cerebrospinal venous insufficiency (CCSVI), plays a role in multiple sclerosis, according to the researchers. And even if it does, researchers have no way of knowing if blocked veins cause the disease or are a byproduct of it.

The new study was funded by the Canadian Institutes of Health Research and was used by an expert panel earlier this year to help determine whether the federal government should pay for clinical trials investigating the safety and efficacy of the vein-widening procedure. The panel ruled there was enough evidence to warrant clinical trials, which the government has pledged to fund.

Dr. Laupacis and his colleagues analyzed eight previously-conducted studies looking into the presence of venous abnormalities in various MS patients, their relatives and healthy controls.

The studies were all different and some have been criticized for using flawed methods, such as failing to "blind," meaning researchers knew which study participants had MS and which didn't, which could lead to biased results.

The analysis of the eight studies shows a high degree of variability with little consensus, said Anthony Traboulsee, director of the University of British Columbia Hospital MS Clinic.

"It does not give us any new insight into the role of CCSVI in causing MS or the relationship between CCSVI and MS symptoms," he wrote in an e-mail.

Several new studies investigating the prevalence of venous abnormalities in MS patients and control groups are under way, including one by Dr. Traboulsee and colleagues. The publication of the results, expected in coming months, should help shed light on the issue and clarify the role blocked veins play in MS, if any.

Until more solid, credible research emerges, questions about the future of this controversial MS theory will remain up in the air, according to an editorial published with the new CMAJ study. While the new study is a good start, wrote Robert Fox,medical director at the Mellen Center for Multiple Sclerosis at Cleveland Clinic, "much work remains to be done before we can be certain whether [CCSVI]is a paradigm shift…or just another fad."