I have a 3 year old cat and one day he was perfectly fine and the next day he could barely walk. We took him to the vet and they did some blood work on him but everything looked normal. They gave him a steroid shot and pain medication. The next morning his whole body was limp. He couldn't stand up or hold himself upright. We took him to a specialist but they don't know what is wrong. I have ruled out poisons. Please help if you might have some idea to what might be wrong

I know that if cats have fleas really bad that can happen. Make sure he has no fleas.