My dermatologist is the one who sent me to a spine specialist. He explained that some people have referred pain from the cervical spine into the arms. Also, some people have brains that misinterpret the pain as an itch. When the itch is extremely deep, it is often nerve related, not skin related. Remember that we are talking here about rare conditions that do not yet have a true diagnosis of cause. It is the nature of science to postulate hypotheses, one after another, and to test them until we find the cause.