Ringworm-Like Patches With a Negative Fungal Culture
Reader Question
My black lab mix dog started losing a patch of hair on his side. When my vet shaved it, a 6" irregular oval appeared, with a red ring around the edge, and darker pigmented skin in the center. My vet ran a culture, which was negative for ringworm, and we treated the lesion with anti-fungal, anti-bacterial shampoo, scrubbing it daily for one week,then every other day for a 2nd week. It appeared to be healing well, over 2 weeks, with the red ring disappearing, hair growing back, but the darker skin at the center remained. Then, 2 more quarter sized lesions appeared, one close to the first one, another on his other side. My vet said he couldn't identify the problem, and suggested a thyroid test. My 58 pound 8 year old dog has also gained about 8 pounds in the past year with no change of diet. Any ideas?
Answer from Our Team
A negative culture makes ringworm less likely. Ring-shaped patches with darker skin can also be caused by bacterial skin infection, which can spread outward in rings with a red edge and darker skin in the center, and often comes back if an underlying problem isn't found.
Weight gain without a diet change, coat changes and repeat skin infections are classic signs of an underactive thyroid, so the thyroid test your vet suggested is a good idea. A skin cytology or biopsy can help if the patches keep appearing.
See ringworm in dogs.
This is general information, not a diagnosis. Please follow your own vet's advice.
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