--an MRI of the spine to look for demyelinating disease? MS and other demyelinating conditions do not only strike the brain (though it's good to have a clear brain MRI).

It's possible that you have neurological symptoms as part of a whole systemic package (indeed, it seems as if your symptom list includes more than the neurological) that may be secondary to a metabolic or toxic disorder (any chance of exposure to nasty substances?). The sad fact is that many neurological symptoms caused peripherally vs. centrally can "fell" exactly the same, which is why investigation is often long and process of elimination in nature.

We have a list of tests and protocols for investigation at the top of this board in the Useful Websites "stickies", but a good place to start is with the Liza Jane spreadsheets at www.lizajane.org. Good tool for seeing what tests are available, which ones you've had, and tracking results patterns over time.