nerve disease?!?! help...

my male cat, Maximus, is almost 4 years old. since he was 6 months old, he has been having on and off problems with his back legs, he will lose complete motor skills and any feeling in them to the point of paralysis. i've been taking him to the vet as regularily as my budget allows, and found a medication (dexamethasone) that helps him to walk again. but it's not permenant. Specialty vets have ruled out cancer and spinal disease, but they haven't told me much more then that! Max doesnt walk (he waddles), or jump like normal cats should, and sometimes he will have fits of twitching. In which case he moves frantically around like he is in pain, and is constantly licking his back area and paws. for this reason i think it has something to do with his nerves. If anyone has heard of a condition like this, or knows why this is happeneing, pleeease help me understand. Max has seen 4 different vets so far and none of them have anything helpful to say or do for Max, except sign a prescription so he can walk. and only the last vet had something to say about nerve damage. if it helps, Max is a black and white tabby cat, and believed to be part Maine Coone.

The waddling and not being able to jump sounds like cerebellar hypoplasia. I don't know if it causes episodes of complete paralysis though. If you do a search on youtube for feline cerebellar hypoplasia it will bring up some videos of cats with it. It is neurological and there is nothing that can be done for it but as long as a cat is still able to eat they are fine. The bouts of complete paralysis though sounds like something different and I would think that a feline vet would diagnose it just by watching him. Though not real common it isn't rare either.