Even though Canadian researchers found that a considerably higher percentage of MS patients have CCSVI (chronic cerebrospinal venous insufficiency), they still do not know whether CCSVI causes MS or whether there is just a higher rate of CCSVI among MS patients for another reason. The scientists reported their latest finding in CMAJ (Canadian Medical Association Journal).
CCSVI, also known as CCVI or chronic cerebrospinal venous insufficiency is when blood from in the veins which drain the central nervous system are compromised. The term was coined by Paolo Zamboni in 2008. Blood from the brain and spine has trouble getting back to the heart - CCSVI is a chronic (long-term) problem.
The problem is caused by stenosis, narrowing of the veins that drain the spine and brain - resulting in a much longer period for that blood to return to the heart. The blood can reflux back into the spine and brain, edema can occur, and red blood cells and fluids can leak into other tissues of the brain and spine. The blood stays in the brain too long, leading to slowed perfusion (a delay in deoxygenated blood leaving the head), causing hypoxia in the brain. Hypoxia means lack of oxygen. Plasma and iron and other undesirable cells can cross the blood-brain barrier, causing damage.
Zamboni hypothesized at the time that CCSVI played a role in causing MS (multiple sclerosis).
Some studies have not been able to replicate Zamboni's findings - that CCSVI is more prevalent among people with MS.
Scientists from St. Michael's Hospital, University of Toronto, and Sunnybrook Health Sciences Centre, Toronto, and the University of Calgary, Alberta, carried out a meta-analysis - they examined 8 studies that had been carried out in Jordan, Germany, Italy and the USA - and compared CCSVI frequency in patients with MS and without MS.
Some of the studies were incomplete while others were small, as were descriptions of the training of those carrying out the ultrasound studies. None of the studies reported whether those performing the ultrasound scans were working blind or not (whether they knew whether each patient had or did not have MS).
CCSVI rates varied enormously among multiple sclerosis patients across the different studies, from zero per cent to 100% in the one Zamboni carried out. Some studies found higher CCSVI rates among those in the MS groups, while others found no difference.
When they gathered the data from all the studies and combined them, they did find a significantly higher rate of CCSVI among those with MS.
Dr. Andreas Laupacis, Li Ka Shing Knowledge Institute of St. Michael's Hospital, Toronto, wrote:
"We found a strong and statistically significant association between chronic cerebrospinal venous insufficiency and multiple sclerosis. However, the large amount of heterogeneity among the study results prevents a definitive conclusion. The source of the heterogeneity is not clear. It is not obviously caused by differences in the definition of chronic cerebrospinal venous insufficiency, patient characteristics or the methodologic quality of the studies.
We also could not identify any factor that accounted for the large and problematic difference between the studies in the frequency of chronic cerebrospinal venous insufficiency among patients with multiple sclerosis."
The authors believe the discrepancies in CCSVI rates were mainly due to the size of some of the studies, they were very small - also, there were some serious differences in techniques used for ultrasound as well as quality control. For studies involving ultrasonography, the training and competence of the operators is crucial.
The authors cautioned:
"(a link between CCSVI and MS) does not mean that the condition
causes multiple sclerosis."
All we know now is that CCSVI is more common among MS patients - this could be simply because of that, there is a higher risk of CCSVI with MS, or that CCSVI raises the risk of developing MS - nobody currently knows for certain which one it is.
The investigators wrote in conclusion:
"Further high-quality studies, using identical ultrasound protocols, are needed to definitively determine whether chronic cerebrospinal venous insufficiency is more frequent among patients with multiple sclerosis than among those without it."
Dr. Robert Fox wrote in a related Commentary in the same journal:
"The meta-analysis by Laupacis and colleagues is a good starting point; however, much work remains to be done before we can be certain whether chronic cerebrospinal venous insufficiency is a paradigm shift in the classic sense. . . . or just another fad."
Written by Christian Nordqvist