i would go to dermatologist and have a skin culture done and maybe even a punch biopsy as they take a piece of skin and send it out to be tested to see what exactly this is and on a culture they do a skin scraping send to lab and have analyzed but punch biopsy is two stitches and culture is no big deal my allergy yorkie has had that to get the right antibiotic for her staph infection
here is apolecia
Alopecia in Dogs