--the chemical toxicity and hereditary possibilities.

You did say you've had about "every test there is". Not to doubt you, but I bet there are some tests out there you haven't had. It is very rare that anyone gets a very complete work-up specific to neuropathy, especially when the more common culprits--spinal problems, central nervous system diseases, glucose dysregulation, obvious infections--have been ruled out. That is due to most neurologists not being specialists in neuropathy specifically, and not knowing about some of the more advanced testing that is available at specialty centers--particularly hereditary tests and those for specific autoantibodies to peripheral nerve.

As I often do with new posters here, I urge you to look at the Liza Jane spreadsheets:

www.lizajane.org


These were designed to be about as comprehensive a list of tests for neurological symptoms as the many minds here could think of, based on extensive research. You can check to see what you have and haven't had, and the spreadsheets are also good for tracking test results over time, to look for patterns.

There are some tests that can reveal hereditary causes of neuropathy--with the Human Genome work ongoing, this is a rapidly changing/advancing field. The most comprehesive updated list I know of is that of the Washington University/St. Louis neuromuscular database (a good resource for everybody to know):

http://neuromuscular.wustl.edu/time/hmsn.html

http://neuromuscular.wustl.edu/synmot.html

http://neuromuscular.wustl.edu/time/hsn.htm

From what you've written, your symptoms are mostly painful, mostly sensory--do the nerve conduction studies show motor difficulties as well?--and the slow upward progression coincides with nerve "die-back", which is a common presentation (nerves farthest from the body center are affected first, and later those somewhat closer).

Can you share any of the nerve conduction tests results?