--to have gluten intolerance presenting as neurological symptoms; jcc's The Gluten File has a lot of information on this (especially that compiled by Dr. Hadijvassiliou):

http://neurotalk.psychcentral.com/thread1872.html

Also, a vitamin B12 level between 500-600 is borderline to me (especially if you're NOT vegetarian); there have been reports of people having symptoms of B12 deficiency at times even with levels up to 700; it depends on how much active B12 is being used (whether there are methylation problems, for example). The homocysteine and methylomaic acid (MMA) tests might be more accurate indicators of whether you're actually at good levels of usable B12.