My guess is your vet hopefully ruled out mange, or any other mite/skin problem. So, with meatball he started getting some thin spots here and there last year. We figured out it had to do with a mix of dry skin( why he scratched so much) and some food allergies. Meatball and salmon don't mix! I started putting olive/coconut oil in his food, and stayed away from salmon foods. His hair never fully returned as thick as it was, but the thin spots are covered. Also, Meatball gets very itchy after a roll in the grass as we'll. hope this helps a bit. Your bully is too CUTE!