Studies that examined the possible link between vein blockages and multiple sclerosis are so inconsistent that it's impossible to reach a firm conclusion about the controversial theory, a new review has found.
Overall, the studies found the blockages known as chronic cerebrospinal venous insufficiency, or CCSVI, are found more often in people who have MS than those who do not.
But a team of researchers and physicians lead by Dr. Andreas Laupacis of St. Michael's Hospital in Toronto said more research was needed.
Italian Dr. Paola Zamboni has suggested that MS may be caused by blockages in the veins in the neck, causing iron deposition in the brain, which triggers an autoimmune reaction. He proposed that unblocking the veins by mechanically widening them improves the symptoms of MS.
Canadian researchers analyzed eight published studies carried out in the United States, Germany, Italy and Japan that used ultrasound to diagnose CCSVI and compared MS patients with non-MS patients.
They found the quality of the studies varied and there were large differences in the results. In general, the studies were small and had incomplete descriptions of the training of those conducting the ultrasounds. None of them reported the degree to which the people conducting the ultrasounds knew whether the subject was an MS patient. Some of the studies found no difference in the frequency of CCSVI between MS and non-MS patients while others found large differences.
When the results of all the studies were combined statistically, CCSVI was found more frequently in those with MS than those who did not have it.
The analysis of the studies was financed by the Canadian Institutes of Health Research. Portions of the study were published today in the Canadian Medical Association Journal.
Dr. Laupacis, executive director of the Li Ka Shing Knowledge Institute of St. Michael's Hospital, said there is great controversy over whether CCSVI causes MS and people on both sides of the issue tend to focus on the research that supports their position and ignore research that supports the other. That's why his team conducted a review of all studies that met certain quality standards.
"The differences among published studies means we can't be definitive at the present time," said Dr. Laupacis, "The overall findings suggest that there may be an association between CCSVI and MS. However, the differences among study results and the poor quality of some of the studies means that more research still needs to be done."
Dr. Laupacis said even if CCSVI is found to be more common in MS patients, that doesn't mean CCSVI causes MS; it may be that MS causes CCSVI.
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