As I commented in your post on the New Member thread; I'm glad you have some answers and a direction in your diagnostic journey.

You have lots of questions, so I'll just touch on the autonomic for now.

First the autonomic system IS part of the peripheral nervous system. So it's likely that if there is any autonomic dysfunction it's coming from whatever is causing the PN, not the other way around. That said, I didn't see anything on your original list of symptoms (in the new member thread) that are typical of autonomic dysfunction, other than GI motility and that test was negative twice.

The usual presentation of autonomic dysfunction includes, GI motility, postural BP changes, fluctuating heart rate/rhythm (tachy/brady), temperature regulation problems, balance, difficulty initiating urination, sexual dysfunction. Even vasospasms and livedo reticuaris (also caused by spasm) are also due to autonomic dysfunction.

It sounds like you have more sicca & PN symptoms, than autonomic.

About treatment of autonomic issues. Some systems affected can be treated...like motility meds/diet changes for gastroparesis. If your GI problems are a motility issue and just mild enough as not to test positive, then simple diet changes may be helpful. I have gastroparesis, and take medicine, but also get benefits from diet changes like: eating small soft low-fat meals (never in the late evening), avoid raw fruits/veggies/nuts, stay upright after eating, and most important--grinding up food (called mechanical soft diet).

Not all autonomic dysfunction can be treated, but some, particularly GI & cardiac aspects have several options.

I would get the MRI's you mentioned and discuss the skin biopsy with your doctor based upon the EMG findings.