I also suffered from upper back itching and dry patches. I think it could be related to fleas from my long haired dog. Mine also feels like it is spreading. I just ordered a product called Cedar Cide...it is all natural and you can watch the video. GO to cedarcidestore.com and check it out.
I had the same thing...very itchy back that seemed to be spreading. Dermatologist said it was just dry skin and to use cream after showering. She suggested CeraVe (I actually bought Eucerin Calming Cream) because it was cheaper. It's working...no more itchy back.