Cat won't use back legs

[caseyenglish92]

About a week ago my cat quit using his back legs he just drags them. his legs do work I can stand him up and he will stand for a bit but if he moves will start dragging them. He will also tense his legs if I push on them and he will curl them when sleeping or stretching. I've checked he doesn't seem to hurt anywhere. I took him to the vet but after several tests including X-Rays and blood tests they told me was he had some fleas (I give him flea meds every month but recently they haven't been working great been trying different ones) and was a little a anemic and constipated (they gave meds for the constipation and he is fine in that regard now) when asked about his legs they pretty much said they don't know. they said he had a little arthritis but I don't think that would make him just suddenly stop using his back legs. He seems ok sleeping good and purrs when petted or held. He is using the bathroom now but since he doesn't use his back legs makes a mess. I'm not sure where to go from here if anyone else has had this happen and knows what it could be please let me know.

[susand]

I am not a vet, but if this was sudden onset my first thought would be aortic thromboembolism and I’d get an urgent second opinion from another vet to rule that out. If It’s something that has come on more slowly over several months, there are probably numerous causes but arthritis is likely the commonest.