--B12 taken orally in megadoses, preferably the methylcobalamin form (designed to be already in usable methylated form and bypass any genetic defects in that chemical process that some people have) would be a convenient, and likely cheaper, way to go. I'd start with at least 5000mcg/daily and have B12 levels (and homocysteine and methylomaic acid levels--the latter are more accurate indidcators of B12 deficiency) taken right before, if I could, and then have those repeated regularly.

One side note--even if you fix the B12 deficiency (assuming that's what you have, and it's causing the symptoms--you really need a good medical work-up), central pain tends to be a recalcitrant beast.