Ask if this neuro specializes in PN.
Most neuros don't, and don't know how to treat it properly.
Ask for a xerox copy of test results before you leave the office.
Pay for them if they charge. You should be able to do this is you're real nice to the nurse/receptionist/secretary.
B12 at 239 is really low. It should read in the 700-1000 range.
The cyanocobalamin is probably a waste of time and expense, it is not easily absorbed by the body and is excreted 99%.. The Methyl cobalamin form, sublingual - is the best form to take, and can be take in large doses without ill effect.
5000 mcgs isn't too large a dose.