Sparkly, if you are concerned tht you do have a B12 deficiency that isn’t being picked up by standard serum testing you may need to ask your GP to do test your serum homocysteine and methylmalonic acid levels. These are very specific tests for B12 deficiency and will pick it up even if the levels are being masked by folate levels or dietary intake of B12.
Karen2 is correct in what she is saying that B12 deficiency CAN be under diagnosed but that more refers to the general population, especially the aged and vegans. The reality is that in the diagnostic process of MS we are subjected to a battery of blood tests designed specifically to rule out exactly this issue. Also it is fairly rare among the general population to suffer severe CNS damage from Vit B12 deficiency because most people are diagnosed with it and treated before it gets that severe. I am sorry that you were misdiagnosed, Karen but to then extrapolate from that that most of us are also possibly misdiagnosed is as I said before, taking it a bit too far.
B