Golden Retriever hair loss

Question
I have a two-year-old Golden who slowly,but steadily, appears to be losing his coat. He has two 12-inch strips on each side that are about naked down to the skin. I've taken him to the vet who tested him for a serious disease (sorry I can't remember which one) that came back negative. She now suspects it's a cosmetic problem. Can you recommend any treatments to reduce/eliminate hair loss?

Answer
The dog is most likely itchy.  Goldens are known for their severe skin allergies.  If the vet checked the dog for mange and it was negative, then I would ask for a short (2-3 weeks) course of some cortisone pills or a shot so that the dog can stop the itching.