--though a serum protein electrophoresis was done, this may not be specific enough to check for monoclonal antibodies, or M-proteins, which are rogue antibodies that cross react with some nerve epitopes and are known to cause neuropathies:

http://neuromuscular.wustl.edu/antibody/mprotein.htm

To detect these one should have the more focused immunofixation electrophoresis of serum and urine done, along with an immunoglobulin enumeration (to see how much IgG, IgA, and IgM you have--this is usually done along with an immunofixation).