Our 13 year old cat is having muscle spasms in her left hind leg. It comes on without warning and she just waits for it to stop and then goes about her business as usual. She doesn't limp before or after and doesn't seem to get upset before or after. It lasts about 5-10 seconds. We have been told by other people that it must be arthritis or such. She is an outdoors cat. In the spring and summer she spends most of the day outdoors and the nights at home. The weather has been changing and she seems to be changing also. She is not eating as much as she used to. G. Kurdziel