The best know cause of PN and AN is diabetic neuropathy, and as well injuries to the spine and brain. I think the idiopathic could be related to autoimmune, as many have posted here, thier PN is often accompanied by an autoimmune disease, but nobody knows the mechanisms behind it. i READ somewhere, that idiopathic could be related to glucose intolerance or pre-diabetes, Most people would suspect neuropathy and full-blown diabetes, not the pre-cursor diseases though.