An MRI may not be a bad thing. I would have it done just in case there is something that they have not caught. You do raise a very intresting point, and I often wonder the same thing meself.

Where does sensory PN end and motor PN begin. People with small fibre seem to have alot of pain,cramping and twitching. people with large fibre sensory have balance problems,numbness,and loss of position sense.

There seems to be alot of overlapping in symptoms. I have small fibre PN,and have had tons of cramping,and now occasional twitching.

I could probably use an MRI meself it's been over 2 years since me last one.