I read that the dorsal root is usually damaged in the lumbar spine, for me the damage just seems to be to the Thoracic spine...

Damage to the dorsal root is not always something you would 'feel' like a back injury. I have damage to the dorsal root confirmed by a new MRI that specifically looked at the DRG and it was bilaterally enlarged and had increased signal...both consistent with ganglionitis. In my case it is from Sjogren's, in which autoantibodies have attacked the DRG causing PN (pain, sensory loss, allodynia, and loss of proprioception). It's not like I have a back ache...the damage is internal.

That makes sense, since we are talking about antibodies, they can attack anywhere. is there any procedure that will reverse the damage to the dorsal nerves? Or is it one of those diagnoses that have no cure?

No, sorry to say, there isn't. But getting the autoimmune disease under control will help slow progression. IVIG can also help halt progression of neuropathy in AI disease.

This is why it's so important to look for cause and treat early.

Correction: the Neurologist did both the Epidermal nerve density and the sweat gland nerve density tests, (I just got the bill, another $650)
On the calf, the epidermal nerve count was normal, but with the swaet gland nerve density is was low normal, by just one point. The sweat gland nerve density would signal Autonomic small fiber neuropathy. I was going to ask him about the sweat test, but I guess this is similar.
Has anyone gotten this done?it is a fairly new test, I don't think it is fully recognized as a "gold standard"yet.

Testing of autonomic fibers from skin biopsy is not new. It does provide a good indication if there is autonomic dysfunction. BUT, there are more precise autonomic testing that is done if the patient is experiencing autonomic symptoms. QSART, and thermoregulatory sweat test are more specific in some ways...and there are also many cardiac testing for autonomic dysfunction (tilt table, 24 hour BP, etc).

Although autonomic function also comes from small fiber nerves, there are autonomic ganglia along the spine. The autoimmune process can attack this ganglia, just like the dorsal root ganglia.

Do you have autonomic problems?