The FDA is warning health-care professionals and patients that injuries and deaths have been associated with the use of the experimental procedure, which involves widening veins in the neck and upper chest.
The therapy was devised by Italian physician Paolo Zamboni, who has suggested MS may be caused by narrowed veins that prevent blood from properly draining from the brain, resulting in iron deposits that damage neurons. Zamboni calls the condition chronic cerebrospinal venous insufficiency, or CCSVI.
His treatment uses balloon angioplasty to open up the veins, in the same way coronary arteries narrowed by plaque are unblocked. But unlike Zamboni, some doctors doing the procedure also use tube-like devices called stents to prop open the blood vessels.
In its warning, the FDA said it received reports of one patient who died from bleeding in the brain and another who suffered permanent paralysis from a stroke after the treatment.
Since receiving those reports in April 2011, the agency began gathering information from outside sources about the risks and benefits of the procedure, including case reports from medical journals.
Other serious complications found include: at least one other death; stents migrating from a vein to another part of the body, including the heart; injuries to veins; blood clots in the jugular vein or in the brain; cranial nerve damage; and abdominal bleeding. The frequency of such complications is unknown, the FDA said.
"After gathering and considering all of this, FDA determined that there was sufficient information to send a safety communication to educate health-care providers and patients about the risks associated with these procedures and to encourage informed treatment decision-making," said spokeswoman Michelle Bolek.
"Because this treatment is not approved or cleared by FDA for this use, we are not aware of how many health-care providers are using it."
At least two Canadians have died from complications after undergoing the therapy, one in Costa Rica and the other in California. While exact numbers aren't known, a few thousand Canadians are reputed to have paid out-of-pocket for the treatment in clinics outside Canada, with varying results.
Multiple sclerosis is a progressive disorder that causes injury to neurons in the brain and other cells of the central nervous system, resulting in what can be significant and disabling neurological symptoms. The underlying cause of MS has not been determined, but the disease is known to have a strong immunological component.
The FDA said studies exploring a link between MS and CCSVI are inconclusive, and the criteria used to diagnose CCSVI have not been adequately established.
"Because there is no reliable evidence from controlled clinical trials that this procedure is effective in treating MS, FDA encourages rigorously conducted, properly targeted research to evaluate the relationship between CCSVI and MS," said Dr. William Maisel, chief scientist and deputy director for science in the FDA's Center for Devices and Radiological Health.
"Patients are encouraged to discuss the potential risks and benefits of this procedure with a neurologist or other physician who is familiar with MS and CCSVI, including the CCSVI procedures and their outcomes," Maisel said in a release.
The FDA said it is informing doctors and researchers that if they want to do clinical trials on CCSVI, they must comply with FDA regulations. Balloon angioplasty devices and stents have not been approved by the FDA for use in treating CCSVI — and the same is true in Canada
Many Canadian MS patients embraced Zamboni's theory after it first made headlines in late 2009. Advocates soon began lobbying the federal government to allow his procedure to be done in Canada, or at least to set up clinical trials to test its safety and effectiveness.
Taking a go-slow approach, federal Health Minister Leona Aglukkaq announced in June that she had accepted a recommendation of an expert scientific panel to undertake a small-scale Phase I/II clinical trial on CCSVI, with the aim of determining the safety of venous angioplasty and to gather better evidence on patient outcomes.
"I've always said that we'll make decisions about this treatment based on the best scientific advice available," Aglukkaq said in an emailed statement Thursday, following the FDA warning.
"Before our government will give the green light to a limited clinical trial here in Canada, the proposed trial would need to receive all necessary ethical and medical approvals."
While the Multiple Sclerosis Society of Canada said it supports the FDA recommendation that further research is needed to understand the link between CCSVI and MS, "we respect and honour the right of people living with MS to make their own treatment decisions," the organization added in a statement.
In 2010, the Canadian society and its U.S. counterpart earmarked $2.4 million for seven studies — now about halfway through completion — to investigate the potential relationship of CCSVI and MS. The group has also committed $1 million toward the federal government's Phase I/II trial.
Canada has one of the highest MS rates in the world, at 240 per 100,000 people; an estimated 55,000 to 75,000 Canadians have the disease.
On a per capita basis, Saskatchewan residents are among the most affected in the country. The province is the first in Canada to go ahead with its own clinical trial and has committed $2.2 million to send 86 patients to participate in a study at the Albany Medical Center in New York state.