My cat is sick, lost weight, and has a swollen, limping leg. Why?
Poor Tommy! I would recommend returning to your vet for a follow-up. The swelling on Tommy's leg does not sound good, especially combined with the other symptoms you have reported. One possible cause of the swelling would be some kind of infection. However, since Tommy has also lost a lot of weight and has been off his food I worry more about a cancerous process such as lymphoma, or perhaps a bone mass. Your vet will be able to do bloodwork and X-rays, and likely will want to take some fine needle samples of the 'knot' to look at under the microscope. They may want to send these samples out to be looked at by a pathologist too. Treatment options can vary depending on the findings of the diagnostic tests. They could range from surgery, to oral medications, to injectable chemotherapy.
I hope you are able to get to the bottom of things soon for Tommy and that he starts feeling better.
Updated on September 23rd, 2025