Cat with rear leg weakness

Question
I have a 11 y.o. female cat.She started limping one day with no pain.Gradually,over about two months,the mobility of her hind legs lessend.The left hind leg is very weak the right a bit better.NO pain even when I touch her legs. She uses her litter box without a problem and is fine with drinking and eating. Our Vet tested her for diabetis.Her sugars are normal.This cat had radioisotope treatment for hyperthyroid about a year ago.That was successful. On x-ray our vet saw a bit of a mid back spinal problem but minor and didn't think it was the cause of her weakness. We are stumped! Can you think of anything this might be.She is strictly and indoor cat.
Anything you can add would be greatly appreciated.
Lucille

Answer
You have ruled out two of the more common causes of peripheral neuropathy in cats, Diabetes mellitus and Hyperthyroidism(by virtue of treatment). Another possibility is spinal lymphoma which is a type of cancer that can show up anywhere in the body, including the brain and spinal cord. This would have to   be diagnosed by MRI. Other diseases affecting the spinal cord include disk disease or a fibrocartilagenous emboli(more common in dogs, I am not sure of the incidence of this in cats?). It is also possible that this is an idiopathic peripheral neuropathy that has no know underlying cause. Is there a neurologist in your area or somewhere you can go for an MRI? This would help you rule out some of the other causes. Perhaps running blood work again would also be a good idea.
Dr. G.