Donnchadh, keep the faith, I know that you will prevail!!
As far as a placebo--well I take Lexapro and feel better, placebo? I shoot copaxone, don't feel better or worse, placebo? I drink orange juice and haven't had a cold, placebo? Well you can see where I'm going with this. Anything can have a placebo effect.
Having a blockage can't be good whether it effects MS or not. I think it causes at the very least a medical problem that should be taken care of no matter is you label it!!