jules i think i've told you this before, but...
general anaesthesia can cause b12 deficiency because of the nitrous oxide aspect.
b12 deficiency alone can cause subacute combined degeneration of the spinal cord
you need to get a series of tests on some nutrients, in particular the ones that are the usual suspects in ms, d3 since it's associated with so many nasty illnesses that you just don't want, including ms, and also nutrients that get depleted by stress (magnesium is one, and you should get both plasma and RBC magnesium tested, muscle magnesium is a decent idea too but we won't go there) and
by sedative drugs and general anaesthetic.
if you're having nitrous oxide and/or general anaesthesia any time a needle approaches, the nutrient depletion aspect is a reasonable thing to have looked at.
taking 100mcg b12 per day is not going to cut it. when my b12 was down, i took 1000mcg per day and even though my b12 level got sorted, the neurological issues did not improve until i added a LOT of bcomplex for a few days, and for that matter quite a lot of vitamin E too.
go to google scholar http://scholar.google.ca/
and search on:
nitrous oxide subacute combined degeneration
there are 856 results.
taking a quality multivitamin/multimineral, a good b-50 complex, 1000mcg sublingual b12 per day, at least 2000IU vit d3, a good calcium/magnesium liquid, and an antioxidant blend with 2g vit C and 800IU vit E per day, and 25mg zinc would be a step in the right direction. none of those will do you any harm, and might well do a lot of good.
check out the links in my signature for additional supplement information