--and, in fact, can be secondary effects of all the anti-nuclear antibody and rheumatoid factor conditions:

http://neuromuscular.wustl.edu/antibody/pnimax.html

Your finding of raised immunoglobulins in spinal fluid is fairly inspecific; it would be more important to find out which classes or specific antibodies are there, and/or to be titred for those specific antibodies in serum.

As to determinations of mild vs. not so mild versions of neuropathy, that is usually interpreted through microscopic examination of the affected nerve fibers--how deteriorated they are and over how much of the body that deterioration can be demonstrated. It is not correlated well with degree of symptomology--people with mildly damaged small fiber nerves, for example, can have terribly painful burning and dysesthetic symptoms, as the brain misinterprets the signals from the damaged but still somewhat functional nerves, and some people with completely destroyed nerves have more numbness than pain, as those areas no longer transmit signals.