We're home - she's unsteady on her paws, was sat in wee when I collected her and has one eye pupil that is far bigger than the other......so I'm not overly impressed at the moment!
Vet was lovely and was very good at going through the Xray but was also very apologetic as there is nothing they can do for her. She basically has lesions along her spine - in the lower lumber spine it has bridged a couple of the vertebrae. She is having problems because of how the nerve travels down the spinal canal and at some points the lesions will impinge on the nerve and cause discomfort - which explains why sometimes she can bound upstairs for a few steps and others she can't (I think it depends on her positioning!).
She could have medication but at the moment it doesn't seem appropriate - further down the line it may be more of an option but at the moment as her only issues are getting upstairs and occasional jumping I'm not going to start her on that. She is in more discomfort than pain he thinks.
I'm glad that instinct proved right. This is basically going to be her new normal. She does still have to lose weight as that will help her but on the flip side of that she is now having to have her activity limited a little - she has to be encourage NOT to go upstairs or to jump anywhere. Fortunately she isn't a very active cat anyway but will have to really watch what she does and try to make being low down more attractive than high up!
Ultimately she is likely to get worse but he doesn't know how quickly. It's just a case of monitoring her. Fortunately she's an indoor cat mainly and is very easy to keep an eye on