"Prevalence of extracranial venous narrowing on catheter venography in people with multiple sclerosis, their siblings, and unrelated healthy controls: a blinded, case-control study"
Lancet Oct 9 
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(13)61747-X/fulltext
"Interpretation

This study shows that chronic cerebrospinal venous insufficiency occurs rarely in both patients with multiple sclerosis and in healthy people. Extracranial venous narrowing of greater than 50% is a frequent finding in patients with multiple sclerosis, unaffected siblings, and unrelated controls. The ultrasound criteria are neither sensitive nor specific for narrowing on catheter venography. The significance of venous narrowing to multiple sclerosis symptomatology remains unknown."