Strange dark patches over kidneys

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My old Mastiff has just spent some time at my parents old farm, she loves it their during the summer as it gets hot and claustraphobic in our flat for her. We went to pick her up today and she seems to have developed two dark patches on her back - perhaps over her kidneys? I'm sorry I cant link photos but there are symmetrical and kidney size and shaped - at first sight, I thought she may have got mange and it was patches of thinning hair, but it seems to be the skin underneath going black too.

~Obviously i will be taking her to the vet as soon as we are back friday - but until then, any ideas?

she has changed her medication for arthiritis recently, is it to do with that? She is not scratching or itching it.

Sorry, just to add my parents had only just noticed it so whatever it is, has only recently occurred.

I am perplexed and a bit worried.

Symmetrical hair thinning, especially over the flanks, can be a symptom of cushings disease in dogs. Does she have any other symptoms?

Thanks for your reply, I've just googled cushings disease and yep you're absolutely right, it is an indication. She could well have other symptoms as she is getting on a bit, it's difficult to tell, but she has slowed down, gained a bit of weight, hind legs aren't good . . She does get hot easily and drinks a lot too. She also goes through phases where she is very slightly incontinent.

I will bring this up at the vets- it seems treatable?

Thank you for your help, I think you may have solved it!

There are a few possible causes, hypothyroidism probably most likely. Your vet will probably suggest full bloods which will give hints about whether Cushing's is an issue, but they'll also be able to check her thyroid function. Really treatable!