A B12 deficiency can definitely cause neurological sx and a severe one, even brain lesions. I have read in several places that there is a high incidence of B12 deficiency in MS patients. Here's one blurb although this one concerns a very small sample: http://www.ncbi.nlm.nih.gov/pubmed/1596201

On a related note, get your homocysteine levels checked as well. I started researching this because years ago I was prescribed folic acid for high levels and recalled this after my MS dx. Like low B12, there seems to be a high instance of elevated homocysteine levels in MS patients. (Actually, just saw that one thing about this appears to the right of the link I posted above.)