My dog is seriously ill. What should I do to get a diagnosis?

There are a lot of things that could be causing this appearance to the skin, and it may not be easy or cheap to figure it out. I would recommend that you keep working with the vet. Baseline blood work, thyroid hormone, testing for Cushing's disease, skin biopsies, food trials, flea preventatives, etc may be needed.

There's no way to know for sure from a photograph, but it does look like a bacterial infection. It is important to have this seen by your vet to determine what it is so the correct treatment can be started as soon as possible before it gets worse or is a sign of an underlying problem. Your vet will do an exam, possibly labwork, and based on these results will be better able to tell you what is causing this and how best to treat it.

This could indeed be mange, an allergy or a bacterial or fungal skin infection. Sarcoptic mange and a fungal infection are contagious to people so I strongly suggest you make an appointment with your vet for a skin exam. Your vet will do a skin scrape and look at it under the microscope, hopefully finding a mange mite. He may also take a brush sample to try and grow a fungus in a test tube. Please make an appointment today.

Oh poor guy. It's very difficult to guess what could be wrong from a picture alone. He'd need a skin scrap to look for bacteria, yeast, and parasites to know if any of those are present. I would be concerned about fleas and a flea allergy, and if you could apply a flea treatment to him that could certainly help. I'm not sure what's available where you are, but Revolution and Frontline Plus are two popular options in the US (along with many oral medications which are better but prescription only such as nexgrad and bravecto). Beyond that, I'm not sure what you can do without some testing.

These look to be burns but it could also be an autoimmune disease, fungal disease, cancer, bacterial infection, etc. There is no way for us to diagnose him over the internet just based on some photos. Obviously the home treatment is not working so it is best to have him evaluated by a veterinarian. This needs some testing and some more intensive treatment.

The only way to definitively diagnose mange (Demodex) is by skin scrapings which should be repeated every 2-3 weeks during treatment until 2 negative skin scrapings are found. Make sure that the flea and tick medication prescribed will also treat mites (milbemycin or moxidectin) and keep in mind that the dosage frequency is different for mite treatment than it is for flea preventative. Treatment needs to continue for 1-2 months after there is a negative skin scraping. Steroids are usually contraindicated in treatment of Demodex. Demodex mites are not contagious to other animals so your other dogs may not be affected.

I am afraid more history regarding Skylars clinical signs would be required in order to assess this case in any way. Food sensitivities, mange mites, other parasitic diseases, skin allergies and skin infections are all possibilities but without a full history it is impossible to advise further