I think the "neuropathy " could be from you running 4miles a day, typically people should rest between runs, a few days in between, to give your body time to recover from the run. Running everyday(at that amount) can cause damage to your body. Exercising everyday(like doing crosffit) all the time damages your skeletal, and musculature of your body. No doubt it has an effect on your nerves. To gain benfit from an exercise or run, you should have a few days of recuperation, running everday can negatively affect your ability to exercise in the future. Ive seen an episode that a mother(i think) who was addicted to exercising at least 6 or more hours on the treadmill, she was skinny, with only skin and bones, eventhough she exercise. exercising causes "micro trauma to your skin" and it builds up and you become more efficient at using the muscle. eventually running everyday requires so much energy, and repairing, your muscle or other parts of your body has to shut down to keep up with the demands.
You should also look into autoimmune causes as well, is there a history of autoimmune disorders, vitamin deficiencies(are common amongst people who workout or exercise alot). Try suggesting blood test for those. You should also try to get some sort of scan done, like MRI,CAT, or ct scan to check for structural abnormalities, if its possible. Just lay off the exercise as well.