Why is my dog with Cushing's losing hair in patches after brushing?

One of the things that Cushing's disease affects is the normal metabolism of hair follicles. Normally hair follicles "turn over" or produce hair quickly enough that we don't see areas of hair loss even though dogs (and us) lose hair daily. When a dog has Cushing's disease, the hair follicles are not regrowing hair as quickly as possible. (And often they do not shed the hairs normally.) Cushing's disease also affects their immune system, so it is more likely that dogs will get overgrowth of normal yeast and bacteria that can invade the hair follicles and cause the hair to fall out. So, what I would suspect occurred is that Buttercup had an area of hair where the hair follicles had a yeast or bacterial overgowth that invaded the hair follicles. Instead of shedding normally, those hairs stayed in place and allowed the bacterial/yeast overgrowth to spread until the hairs were mechanically removed with a brush. And since her hair follicles were not regrowing hair normally, the area is now bald. If there is any crusting, itching or redness that develops, I would certainly have your vet examine Buttercup. Otherwise, i would recommend regular bathing and brushing to remove dead undercoat and prevent future skin problems. It will take time, but fur should regrow in that area as long as the skin there is healthy.
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