My beagle Jake had Cushings, with a little pot belly and a little extra thirst. His symptoms were mild and did not require treatment.
At the time the common wisdom was that the treatment was more art than science, and treating it (which was very expensive) could even make things worse. I understand there are new treatments now but I don't know how good they are. We decided to treat his symptoms if needed and just go from there.
About a year later Jake was diagnosed with Lymphoma and the steroids he took as part of his chemo exacerbated his Cushings. The specialist thought they could handle it, but Jake just couldn't. We finally let him go.