Hi there luvmyprecious,
Welcome to Just Answer! I would like to help you and your cat with this question, but need a bit more information in order to better assist you.
Which leg was she not using?
Do the toes on that leg feel cooler than the other toes?
Is she mentally aware and bright, alert and responsive?
Fiona
Ah, so that right back leg has cooler toes than the others?
Can you push on her pads so her nails protrude on that back right? And then do the same on the back left. Please compare the colour of the nail bed (what you can see through the nail that should be a nice pink wedge). Does it look blue-ish on the back right?
Hi again...
I am quite concerned with what you are telling me. The fact that the painful limb is cooler to the touch, and that your girl does not even want you to touch it suggests that this might be a problem due to a thromboembolism (blood clot). This can happen if a blood clot prevents blood flow to the limb by getting caught in femoral artery that feeds the leg. Most often these blood clots are caused by underlying heart disease.
Even if your vet has reporeted no heart murmurs your girl could still have had heart disease, but so mild there was no murmur. Let me explain....
When I hear a murmur while auscultating the heart, it tells me that there is turbulent blood flow within the heart. Think of a stream - if it is flowing smoothly, you can hardly hear it. But if there are lots of rocks and a waterfall, there is turbulence and now you can hear it.
The same is true of the heart. When there is turbulent blood flow, a blood clot or thromboembolus may form. Your girl may have a very soft murmur that could not be heard, but is still causing clots. This blood clot can leave the heart in the large blood vessels exiting the heart, but then get stuck in many of the smaller blood vessels leaving those major arteries. When this happens, it can cut off blood supply to a limb. Suddenly the cat limps on that limb and is very painful.
Think of wrapping an elastic band tightly around your finger. Pretty quickly it becomes painful and it is hard to use the finger. This is essentially the same thing that happens when a thrombus blocks blood supply to a cat's limb.
On exam, these kitties present with pain and limping. If the clot has gone to the right front leg (the first "exit" from the major arteries) that foot will be colder than the others and the nail beds will be blue. The blood clot may lodge in the caudal vena cava, which is a major blood vessel leading to both back legs. In this case, the cat will not be able to use the back legs but will drag them around and will be in severe pain.
If the clot has gone to the right hind, then you will see this problem just on that limb.
The concerns for your cat are that this is painful, AND that if there are more blood clots in her heart, if they leave at any point and she gets a maojor clot to both hind legs, that usually carries a grave prognosis.
Early treatment involves drugs to stop more clots from forming - the choices are aspirin or coumadin (rodenticide, rat poison, warfarin). Unfortunately, if there is a major clot to both back legs, treatment may not be possible.
Here is more about thrombus formation in cats:
http://www.petplace.com/cats/aortic-thromboembolism/page1.aspx
http://www.peteducation.com/article.cfm?cls=0&cat=1540&articleid=3286
http://www.thepetcenter.com/sur/saB.html
And more about Hypertrophic Cardiomyopathy which is the most common heart problem in cats, and the most common reason they develop blood clots:
http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=2507
Because of the very serious possibility of a major clot going to BOTH hind legs, I would urge you to have your cat seen immediately by an emergency veterinarian. The vet could check to see if it is safe to put your cat on aspirin - not a drug we use often in cats. Also, the vet could advise you on how to massage your cat's leg and use heat to try to improve circulation in it. Stronger pain killers might be prescribed.
I know you were hoping to wait to see your own veterinarian, but I feel you need to seek immediate attention for this problem!
If this has been helpful, please Accept my answer and leave feedback. I will still be here to provide further information if you need it!
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.
Cat Veterinarian
15 years experience as a companion animal veterinarian in British Columbia, California and Ontario