Q: Have you ever seen a previously healthy cat develop acute limb paralysis? She is a stray outdoor cat, at least 5 years old. She does not appear to be in any pain. No lesion is obvious.
A: It is difficult to answer your question based on the limited information in your letter, namely, whether the limb paralysis involves one, two, three, or all four limbs. For an outdoor cat, I would imagine trauma to be the most likely cause for sudden limb paralysis. Although no external lesion is obvious, a thorough exam by a veterinarian, with emphasis on the neurological system might elucidate the problem. Trauma involving the limb is often obvious; however, trauma involving the spine may show no external lesion.
A common cause for acute onset of rear limb paralysis is arterial thromboembolism, that is, a blood clot. Some cats develop a heart condition called hypertrophic cardiomyopathy (HCM). This heart disorder increases the risk of developing a blood clot within the left atrium, one of the chambers of the heart. Occasionally, a piece of the clot will break off and travel down the aorta, and will lodge at the very end of the aorta, where it branches to supply blood to the rear limbs. Cats will become acutely paralyzed in the rear limbs. This is a painful, devastating condition, with a very guarded prognosis. The fact that this cat does not appear to be in any pain makes thromboembolism a less likely diagnosis.
I hope this cat is tame enough that you can catch her and see that she gets the veterinary attention that she clearly needs.