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What the heck is wrong with my cat's ear? - ringworm pictures scabs

3 weeks ago, our cat developed a kind of crust on a clear case of his inner ear, which opened and bled. We took him to the vet and after a thorough examination found the vet said there were more sharp and deeper into your ear canal. It was proved by the ear mites and lichens, which were negative. The bark is white / gray in color. The vet said he was also a secondary yeast infection and gave us to treat Tresaderm. Since the poor cat has been quarantined to avoid spreading what he has with the rest of the family, because we do not know what it is. The cup itself is completely healed, but there are still deep in the earth's crust.
"It is an indoor cat, revolution, mites, fleas, and has taken, most of worms.
OrUR showed veterinarians in veterinary hospitals (animal and therefore is not for a second opinion) and send photos to a dermatologist who said it looked like something viral, but to be sure that our cat was sedated and biopsy. It is a question of cost, but I want to save the race, he really hates the vet and be put under sedation.
Has anyone experienced something similar? And what was that?