EMO-Two neurologists, one at Brown Neurology in RI, and a second opinion consultant at Mass. General surmised after numerous tests, that my poly neuropathy was probably an autoimmune reaction, either to spinal fusion surgery, anaesthesia, medication or infection unrelated to surgery. Both recommended iVIG infusions, along with continuing Aquatherapy and clinical PT at URI, our nearby state university.
I have noticed improvement in motion and strength in my legs, and glutes, also in my upper body and core, which helps me walk with a smoother gate on my walker, able to weight-bear more on my legs. Pain has calmed down over time, too.
So, with that experience I would encourage you to search out a neurologist who understands the connection between autoimmune causes of neuropathy and will order iVIG infusions to tamp down inflammation in your nerves. And continue with PT that will work on the brain, balance, muscle, nerve connections. Do what you can, and make sure you have a neurologist or two in your corner. We are there in the meantime.

I feel your 'pain'! I too have elevated FGFR3 Antibodiss along with elevated CSF protein. My dx is Antibody mediated sensorimotor axonal neuropathy. My neurologist made clear that my IVIG infusions were meant to slow the progression of the disease....and they did, until Medicare reversed its approval in April. A dramatic decline ensued. Like you, exercise has helped reduce cramping/pain and I've heard the Gabapentin song. Ugg...it really messes with ones cognition. I had to stop. It seems like all the docs can do is identify our conditions thus justifying for insurance our seeing PT's, Pain Mgt Docs and others in the field. So now it comes down to a mental game. Finding ways to live with our rebellious bodies.