I am sorry that you have not have more replies. Generally it is the accepted wisdom on here to avoid a sural biopsy at all costs, it can leave you with permanent pain and nerve damage. Many of us, myself included, have turned down the spinal tap as unlikely to yield answers after bloodwork, EMG, and a much less invasive and more informative skin punch biopsy are done.

But yours appears to be an atypical case with asymmetrical symptoms that are unusual, so I do not know what to say about the tests. I would ask, since you have had some symptoms for what seems like quite a while, does anyone in your family have neuropathy? If you are not diabetic, have a slowly progressing neuropathy with shortening of the Achilles tendon, it does sound like it could be CMT, a hereditary neuropathy.

Next time at the doctor mention that, and also ask for a skin punch biopsy.
I hope someone more knowledgeable chimes in. I have advanced CMT, type 2, with axonal degeneration.