I would like to know how you tested for "drugs"?
I am not meaning illegal drugs...

I am talking about Cipro, Levaquin, Avelox, Flagyl, Tindamax, statins, and Zyvox, being used now, recently or in the past.
I don't know of any "tests" for these.

There are many drugs used on RX commonly that cause PN:

http://neurotalk.psychcentral.com/thread92116.html
Some of these drugs are used for bladder infections, and upper respiratory infections, including sinuses.

Also solvents from hobbies, or the workplace, or even the solvents that fume out of dry cleaned clothes, have been implicated in PN. Gardeners, who use pesticides and herbicides also have risks.
Outgassing formaldehyde is also problematic in new buildings and homes.

There are over 100 causes of PN ... the trick is to find yours.
When all is said and done, if you have dorsal root damage, there may not be much you can do about it. (until the research catches up with it).

Yes autoimmune neuropathy may be treated with disease modifiying drugs..(DMARDS). IVIG and Rituxan are expensive last resorts.
Some of our posters have Sjogren's syndrome, and struggle with that.
Not all autoimmune suppressing drugs work well, however.