So sorry you have trouble with your back. If you have any nerve compression on the root as you described at L5, that can cause the numbing. If you can go for another opinion, I would do it if your symptoms keep re-occuring. I do know how frustrating problems with your back can be. I am not sure I have heard of problems with numbness from thyroid conditions. I hope others can answer you question too. I hope you can get resolution and that something can be done to help the numbness go away. Consider another evalutaion on L5 by a different physician. If you go to an orthopedic person, try a neruologist, and visa versa. Several fields of expertise. good luck to you and have a good Thanksgiving. ginnie