What Causes Burning Sensation From Shoulder To Arm And Elbow?

I have a constant burning sensation that goes from the top of my shoulder down the side of my are, to the back of my elbow.. The burning increases if I raise my arm straight out my side. Also there are certain points on my arm that I can not touch due to the pain.. almost feels like a severe buise, but nothing is there.. Will an MRI tell if maybe it could be a muscle tear? Carrying anything in my left hand sends the burning down my whole arm... Any suggestions??