Numbness in both feet related to lower back

For approximately 8yrs. I have been under the care of a chiropractor for lower back pain.  At the same time my right toe would go numb.  After treatment the numbness would disapear.  It continued to return and get worse over time.  The numbness went from the toe to my ball of my foot and now goes all the way to my heel.  The latest is now it is happening to both feet.  Lately when I see the chiropractor the numbness lessens but never goes completly away.  Have had an MRI, showing neg. damage, no bolging disc.  Then was referred to complete a MRE, he tested my lower nerves and muscles, found possible neuropothy. Sometimes it feels like a needle going into my toe. Dr. stated neuropothy would not be related to lower back pain.  Why does it improve with back adjustment.  This has been going on forever, need help please.FOS