It is usually caused by a lesion somewhere in the spinal cord. It causes the front legs to go completely stiff and back legs to be useless as well. This happened to my cat on Friday, in one day, without warning. My vet is treating him with cortisone shots, hoping to reduce the swelling in his spine. He can not walk, he can drag his body around. He can still go to the bathroom on his own, but has to have help eating. His head also tilts to one side and flops around. He needs support to do most everything. This is a very sad illness that comes on so quickly. I wish there were more things on the internet about it. I do not know what the treatment is for this and what the prognosis is. My vet says there is a 30 percent chance he will walk again. He has been making small strides. I am sure many vets as well as many owners would put the cat to sleep but I am giving him a chance to live. He eats, and purrs, and he wants to live and walk again.