--to have an isolated small-fiber syndrome just from lumbar compression/radiculopathy; in such cases one usually has evidence of larger, myelinated nerves having been damaged as well. Have you had a full lower extremity nerve conduction/EMG series done, including the paraspinal muscles of the lower back, to try and see if there is signal disruption there?

None of us are excused from being "co-morbid"--one can have lumbar or sacral compression and have other things going on as well. In fact, there is something called the "double crush hypothesis", which theorizes that nerves already damaged by some process can get mechanically compressed and produce symptoms greater than one would suspect from "the sum of the parts".

As far as testing, have you seen the LizaJane spreadsheets at lizajane.org? These were designed to be about as comprehensive a series of possible tests for neurological symptoms as some very wide-ranging minds could come up with; you might want to take a look and see what you've already had, and not had.