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NEW YORK (Reuters Health) - A new analysis of past studies concludes that there seems to be some link between multiple sclerosis and narrowed head and neck veins -- but more research is needed to be sure.
The report, funded by Canadian Institutes of Health Research, is the latest addition to a controversy that has led some MS patients to demand a risky treatment for the blood vessel condition while scientists clamor to figure out whether or not it causes MS -- or if it even exists at all.
"The message in some ways I'm sure is kind of frustrating," said Dr. Andreas Laupacis, the lead author of the new report from St. Michael's Hospital in Toronto.
"There's some tantalizing evidence that there might be something here, but we still don't know."
The authors of the study were cautious because they could only find eight studies that have looked at how common the condition, known as chronic cerebrospinal venous insufficiency, or CCSVI, is in people with and without MS.
Italian researchers first proposed in 2009 that MS, typically thought of as a disorder of the immune system, might actually be caused by blood vessel changes.
Dr. Paolo Zamboni's team found signs of CCSVI on every ultrasound of patients with MS -- and in no "control" subjects without the disease.
Their theory was that veins bringing blood from the brain and spine back to the heart sometimes become too narrow, making blood leak back into the brain tissue. That could trigger inflammation, eventually causing the balance and muscle problems seen in MS.
But since then, other scientists haven't been able to show the link between MS and CCSVI quite as convincingly.
To assess the current state of the evidence, Laupacis and his colleagues analyzed the eight studies -- including Zamboni's -- that have compared the frequency of CCSVI in people with and without MS.
Those studies involved anywhere from 10 to 310 patients with MS and a similar number of controls.
The researchers found that people with MS were indeed more likely to have the narrow blood vessels -- about 13 times more likely. And when they removed Zamboni's original study from the mix, the remaining seven studies still showed that CCSVI was almost five times more common in people with MS than without.
But there was a huge range on a study-by-study basis -- including one study that didn't see evidence of blood vessel changes in any of 76 people with or without MS.
That could be because not everyone agrees how to read ultrasound tests to look for those changes, or is trained to see them, researchers said.
"It may well be that the different groups are using different ultrasound techniques," Laupacis told Reuters Health. "It's not a straightforward kind of test."
It's also possible that bias may have unknowingly crept into some of the CCSVI diagnoses, researchers said, if the investigator reading the ultrasound knew which images belonged to people who did or didn't have MS.
Laupacis said that more research is being done that should clarify the picture on how CCSVI and MS are related. Even if the narrowed blood vessels do show up more frequently in people with MS, though, it doesn't mean that a procedure to prop open those vessels, called liberation surgery, would also be a cure for MS symptoms. That surgery comes with a risk of bleeding and infection.
"Just the fact that (CCSVI) is more frequent in people with MS, it might mean that it causes MS. It might mean that it's a consequence of MS," Laupacis said.
"It's a critical next question to be grappled with," said Dr. Robert Fox, an MS researcher from the Cleveland Clinic, who wrote a commentary accompanying the study in the Canadian Medical Association Journal. "If there is an increased risk of CCSVI in patients with MS, what do we make of it?"
Both Laupacis and Fox have consulted for or received funding from pharmaceutical companies that make MS drugs.
Fox said that he often finds patients with MS keep themselves a bit dehydrated, because otherwise they have to go to the bathroom frequently -- and that dehydration might affect how the blood flow in their veins looks on an ultrasound.
Or, "Maybe some of these findings on ultrasound just have to do with a sick brain," he told Reuters Health.
Fox said that until those questions are answered, people with MS shouldn't get an invasive procedure that has unclear benefits.
"I fear that some patients will say this is a vindication of the CCSVI theory," Fox said. "We're still a long way away from feeling that this intervention should be recommended for MS."
SOURCE: bit.ly/qB3Mku Canadian Medical Association Journal, online October 3, 2011.