My neighbors boxer Abbie has that. She has to take a kind of chemo treatment for it. It has only flared up 2-3 times, but when it does she just lays around and doesn't come out of her yard...
. The treatment makes her so sick...and then after her treatment is over she is running and playing again.
The vet said that when dogs have it that it usually flares up during the heat cycle or pregnancy.