I know rheumatoid arthritis emits heat when it is in its active phase. This usually happens on the hands, feet, knees ect. I have no clue as to emitting heat on your back though.
Sorry that I am no help!
Things ruled out- TIA's, Lyme, Lupus, Crones, Narcolepsy, CFS, Fibro, Parkinson's, arthritis, and brain tumors.
Still nobody has answers.
Started my journey 1/06
When everything's coming your way, you're in the wrong lane.