These are questions you need to ask -- no answers coming from me...just questions:
1. Does your neurologist know about the referral to the Rheumatologist? What does HE think? If he doesn't think it necessary, then cancel.
2. Does your PCP know you're seeing the neurologist, and have they talked with each other? Has the neuro told your PCP that there "seems to be something neurological going on", but it can't be confirmed (yet) by usual testing? If so -- then why did your pcp make the referral to the rheumy?
3. Which doctor did your blood tests for rheumatological stuff -- the pcp or the neuro? If those tests did indeed come back "normal", why did they make the referral (or was it made before the tests were run?)
4. How confident are you in your neuro? If you feel confident that he really is trying to figure out what is wrong..and is convinced that it is neurological...then you might reconsider the rheumy appointment. If you don't think either the pcp or the neuro really have a clue about what's going on with you, then you might go.
5. If you DO go, and the rheumy says, "whatever's wrong with you, it isn't rheumatological"...then ask HIM "what next?" or "where should I go, next?". It might give you some direction as to what is ailing you.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....