Hi! How old is your dog? Thinning of the coat is pretty normal as dogs get older. But the bald patches and scabs are less so... I definitely think you should get a second opinion, especially if your vet didn't offer any explanations ....
Here are some ideas that I thought of:
- Allergies (could be to food, environmental allergens, or even certain grooming products).
- Infections (could be bacterial, fungal, or parasitic)
- Autoimmune disorders
- Hormonal imbalances (could be hypothyroidism or Cushing's disease)
- Nutritional deficiencies (could be due to poor diet or nutritional imbalances)
- Mites or fleas (could have led to excessive itching)
- Side effects of medication
I would definitely go see your vet for a follow up, or even go see another vet. A good vet might suggest additional tests such as skin scrapings, biopsies, or blood work to determine the exact cause of the problem. I'm not a medical professional in any way shape or form, so please verify what I'm saying with someone who knows what they're doing!
Hope your dog feels better soon!