Several reviews critical of the CCSVI paradigm have noted that there is a condition called transient global amnesia in which an incompetent jugular valve allows reflux back into the brain. Some authors have suggested that this disproves the CCSVI paradigm because if reflux caused MS lesions then the people with TGA should all have MS. A recent example offers an opportunity to discuss this
From this paper: http://www.ncbi.nlm.nih.gov/pubmed/21765873
Interestingly, CCSVI is reproducibly associated with TGA [Sakai et al. 2010; Chung et al. 2009, 2007, 2006; Schreiber et al. 2005; Sander et al. 2000], which has no known association with MS.
This argument doesn't hold water.
Researchers have been evaluating the problem of TGA and how it might relate to internal jugular vein incompetence for some years and this is still under investigation. The theory is that the valve at the bottom of the jugular vein is incompetent (this has been demonstrated by a number of authors) and this dysfunctional valve allows blood to reflux up into the brain when the person does the valsalva maneuver (a holding of the breath and pushing as if to have a bowel movement). It appears that these incidences of TGA seem to occur in these patients after a bowel movement.
So there appears to be an association and one author even did time of flight MRI and evalauted cerebral blood flow (as in the italicized quote and linked at the paper: Chung 09, 07) several days after an attack. They noted that the patients still seemed to demonstrate a kind of venous congestion related to the left (only left) jugular/brachiocephalic; most of them the reflux was limited to the left jugular vein themselves and localized and only in a minority did it reflect all the way back to the deep veins (Chung 07). They characterized the problem as a kind of "intermittant claudication" focusing on the intermittant nature of the blood flow impairment and low oxygen states.
What is important about this is how it is different from CCSVI. CCSVI is a condition in which there is stenosis that is continuous, not intermittant. This makes a differerence physiologically because the body has some coping mechanisms for shorter term changes in the circulation. For example, researchers have identified that in circulation of the leg people who stand all day see increases of greater than 3 fold in their leg's venous pressure, but if they walk even for a few minutes periodically the pressure will correct itself.
It takes several days of unrelenting increased pressure in the legs for the initial changes that may lead to venous disease to begin to kick in (ie Bergan et al 2006 "Venous Disease"). And even if there is venous disease, it is not always venous insufficiency, which is the severe form of impaired venous circulation. Interestingly even if there is venous insufficiency there are not always open lesions in the lower leg. The point is that reflux itself is not "venous insufficiency".
So that leads back to the question of intermittant reflux due to an incompetent jugular valve and whether that is "CCSVI" as the neurologists stated in the paper critical of CCSVI quoted above. The answer is no, intermittant reflux due to an incompetent valve on one side of the jugulars is not the same as CCSVI. Dr Zamboni confirms this in email to me. I also discuss this issue in greater depth in my book.
If you'd like to check out the book and read some excerpts go to http://ccsvibook.com
~marie