I would say, YES, that full body SFN can point toward ganglionopathy...just as many forms of SFN can point there.

I don't think there is any blood tests to determine whether IVIG will be helpful. If you have documented small fiber damage or decreased density and history of autoimmune disease, then IVIG would be appropriate to try. A 3-6 month course would be enough for you to tell if if would help. Then a repeat skin biopsy would be helpful to gauge any improvement...along with how you feel clincally.

You shouldn't have to "push" for IVIG if you have SFN and autoimmune disease...it should be suggested by your doctor, not you having to push. Maybe another opinion would be best to get you the proper treatment.

Although rapid bowel transit has been known to occur with autonomic neuropathy, the most common is the opposite...lack of motility.

As for the gangionopathy, there is a new MRI/MRN at Johns Hopkins that looks directly at the dorsal root ganglia (DRG). This is how I was diagnosed with gangionopathy (I had noth increased signal and bilateral enlargement of the DRG). I'm not sure (and sort of doubt) if you have this available in the UK, but might be worth asking about, just in case.