I'm wondering if anyone has experienced this. I recently went back to physical therapy because my leg and back muscles still need some work. At the end of a session, the therapist put heating pads on my back. (Pre surgery, I used heat all the time.) After a few minutes I started to feel a weird sensation along my spine and it quickly turned to burning. I had to take the pads off immediately. Later I realized that it had to be the rods and pins conducting heat. I had never felt anything like that in all my years of heating pads.
It never occurred to me that this might be an issue.