In my thirties I developed extreme muscle weakness and depression...it was in all my limbs, but my hands were affected the worst..I could not make a fist, and I could not hold something small, like a needle between my finger and thumb... I was never diagnosed, because i have a terror of hospitals, although there came a time when it was so bad, I actually thought I was dying!  I was unable to stand up without assistance and could not climb a flight of stairs. Then very gradually i semed to improve..there was no reason that i could see for it, but i got back to be able to walk,and could hold a needle again, which was essential for my job at the time (although I had to concentrate on keeping thumb and finger together)  this lasted for about 6 months, then suddenly 2 days ater my birthday I had a total relapse... I could not even get out of bed and i was terrified! I tried to think of any outside factor that could have caused this, and something occured to me. I had at this time been a vegan for 15 years  ( I still am a vegan) I was particularly fond of a yeast based pate that i ate regularly...also i ate yeast extract spread such as marmite every day to keep my b vitamins up. Six months previously.when i had started to improve, my work had become scarce, and so  I had cut back on my more expensive food.the yeast pate was one of these things, as were several TVP products...also containing yeast extract. For my birthday, my mum had sent me some money, and I'd bought some of that pate and eaten a lot of it in one day...I imiediately removed all yeats products from my diet. Within one week I was in perfect health!  this was after 5 years of illness!... I know 100% this is not a psychological thing, because since then i have had slight relapses, and sure enough each time I have tracked it back to having unknowingly eaten something with a yeast product in it. Bread is fine, by the way.... it's just things with the extract in them. I now take b vitamins that are not yeast sourced....I also have recently started to take a vit D supplement... not related to my previous illness, but i am very fair skinned and avoid the sun, so I was told by my doctor that I should do this. I hope this is of help to someone...I also have a close friend who was a doctor and also a vegan. She was diagnosed with MS in her early 40s...when i met her she  could barely walk.she stopped all yeast products and was much improved..She also chose to have all her amalgum tooth fillings removed, and she said this also made a difference.