I got dx'd in 06 and the docs refused to entertain the idea that my b12 deficiency history could be a factor. even though it's a known differential dx. on the one hand my doctor's computer system had a glitch so that my 'undetectable' result was undetectable in itself. on the other I wouldn't do a washout test to prove existing deficiency, because I was terrified. not to mention that the reference range is useless. so yes, b12 deficiency is a well known differential diagnosis for ms, but ime you can have it, have the lab work, and it still won't make a difference in the process. patients have to advocate for themselves for sure.
my approach: no meds so far - just nutrient-dense anti-inflammatory whole foods, and supplements where needed
info: www.whfoods.com, www.nutritiondata.com