A good question! I don't suppose they have because I've asked many times. Initially they thought it was my RA drugs and also tested my serum B12. I assumed it was part of my connective tissue diseases because I have high inflammation in my blood (ESR and CRP). But less than two weeks ago my rheumatologist said that it can't be because my joints have no inflammation and all my autoabtibodies are now negative. Personally I think he's wrong but proving this would be impossible. My rheumatologist did suggest that the neuropathy and dizziness might have an endocrine cause but my GP dismissed this as implausible and has referred me back to neurology. Difficult to know what to do next. I'm stuck I admit!