Despite a few well-publicized studies and many hopeful patients waiting for treatment, there is no good evidence that multiple sclerosis, or MS, is caused by a blood vessel condition, a fresh look at the medical literature finds.
That means patients with MS shouldn't have surgery to open veins that connect the brain and spinal cord to the heart, researchers say.
"It's so appealing, the idea of a quick fix, of a surgical amelioration," Dr. Bridget Bagert, whose findings are published in the Archives of Neurology, told Reuters Health.
But, she added, "It's really not the right thing to do if the problem isn't established as being real."
MS occurs when the protective coating around nerve fibers begins to break down, slowing the brain's communication to the rest of the body. It's typically thought of as a disorder of the immune system and has no cure.
In 2009, however, Italian researchers led by Dr. Paolo Zamboni linked MS to a blood vessel condition called chronic cerebrospinal venous insufficiency, or CCSVI. The theory is that veins bringing blood from the brain and spine back to the heart become too narrow, causing some of that blood to leak back into the brain tissue.
Zamboni and his colleagues figured that might trigger inflammation, eventually leading to the balance and muscle problems seen in MS. Indeed, the Italian team's initial studies suggested that CCSVI is very common in MS patients and scarce in people without the disease.
But three independent studies published since then haven't found a clear link, according to the new report.
"That really casts a lot of doubt on to whether CCSVI exists at all, let alone whether or not it's the cause of MS," Bagert, from the Ochsner Clinic Foundation in New Orleans, told Reuters Health.
After Zamboni's initial findings were published, hopeful MS patients started requesting blood-vessel opening procedures, and a few doctors became well known in the MS community for being willing to perform them.
To determine if a person has CCSVI, a picture of the veins is taken using ultrasound or another type of scan. If the blood vessels look too narrow, doctors may open them up by inflating a small balloon in the veins.
Those procedures are typically used in people at risk of a heart attack, and they come with a risk of complications, including bleeding and infection.
But researchers said it's hard for doctors to even know what they're looking for on blood vessel scans, and whether anything that looks strange could be playing a part in MS symptoms.
"There's still considerable information and understanding that we don't have about this observation" on the role of CCSVI in MS, said Timothy Coetzee, chief research officer at the National Multiple Sclerosis Society in New York.
"There's no question that there has been considerable ambiguity and questions about some of the studies that were 100 percent (in favor of the link) and some that showed nothing," he told Reuters Health.
Bagert said there is also controversy over the methods used in the original Italian studies, which could have let potential investigator bias creep into the findings.
Because of the inconsistency in past reports, the National Multiple Sclerosis Society has spent more than $2 million funding research on how often blood vessel abnormalities show up in people with MS.
"Resolving this issue matters to a lot of people," said Coetzee, who was not involved in the new study.
He added that speculation about possible causes of MS — which has included theories about infections and vitamin D — is nothing new.
And as long as people with MS are well informed about the pros and cons of getting the procedure to open their blood vessels, he's not opposed to patients going ahead with the treatments for now.
But Dr. Ellen Marder of the University of Texas Southwestern Medical Center at Dallas, another author on the new paper, said the data doesn't support that idea.
"We don't think (CCSVI) is the cause of multiple sclerosis," she told Reuters Health. "We would not advise our patients to be tested for this or act on any recommendations based on this sort of testing."