Hi, I don't have any experience with this, but agree with others and Lisa, that this doesn't look like mange, it's not red, doesn't look irritated or infected. I'm wondering if its something as simple as him lying on his elbows, and causing rubbing, and the fur to rub off? It looks like a very localized area. I would keep an eye on it, could be the start allergy symptoms? The vet will be able to confirm. I hope it's nothing serious, and it clears up. Please keep us posted.