I have  seen specialists try diathermy-surgery, and then long term antibiosis with minimal success. The only cases that got better, really, properly better were those put on a sensitivity diet plus high-dose- steroids and metronidazole, usually for about 6-8 weeks. The lesions cleared and the dogs were vastly more comfortable for example  on examination of the area. Steroids are bad? Well not I these German Shepherds they weren't. I was greatly surprised at the speed and efficacy of this regime for something that I had believed to be a deep pyoderma!  Hey ho, you live and learn!