Aortic thromboembolism
Cats may be struck 'out of the blue' by a blood clot resulting in dramatic signs (sudden onset of lameness and pain) and potentially devastating damage. The back legs and the right front leg are most often affected and may be paralyzed. This is an emergency, if you suspect that your cat has suffered a blood clot, you must seek veterinary help as soon as possible.
Feline aortic thromboembolism: pale hind legs © Glen Cousquer