If the attack on the nerves is from antibodies we still don't have tests for, yes, it may be helpful.

They will try it, and if it doesn't work, then you are no further behind.

Certain antibodies produced from bacteria and viruses (and perhaps vaccines), may not show up in standard autoimmune testing. Some autoimmune antibodies come and go and give confusing test results.

If your insurance pays for it, I'd give the IVIG a try. The medical community uses it much more often today, than in the past for many autoimmune inflammatory issues.

Autoimmune diseases may test sero-negative. Patients on myasthenia gravis forum here have tested sero-negative, and several posters here with Sjogren's syndrome have sero-negative results.