If the vets did not test or check for tetanus this is a real possibility for you to look into. Its really uncommon in dogs but it can happen. This site explains some of the symptoms they saw in their dog
http://www.woodhavenlabs.com/tetanus.html
and this site has a good overview of the issue
http://www.provet.co.uk/health/diseases/tetanus.htm
Another possibility is a rabies vaccine reaction if he had one just before all this started. I have heard of some dogs going into paralysis after being given a rabies vaccine. The ones that recovered that I know about went and had accupuncture done.
You didn't mention breed of dog but in Shepherds for example there is a known autoimmune disease called Degenerative Myelopathy where it starts with rear limb paralysis and moves on to front limb paralysis. You can read about it here
http://vetmedicine.about.com/cs/dogdiseasesd/a/degenmylopathy_3.htm
Goldens and Labs both have problems with inherited muscular dystrophy too. You can read about this and other issues here
http://neuro.vetmed.ufl.edu/neuro/lmn_dis/lmn_dis.htm
But ask about tetanus if the vet has not already considered that.
You might also look at this site for help with mobility issues
http://www.handicappedpets.com/
Hope this helps you and I wish you luck with him!
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