The Cat with Blue Claws
Veterinary & Aquatic Services Department, Drs. Foster & Smith

One long-time owner called us because her cat seemed to be weak in his hind legs and could not jump up as he usually could. One thing she said stuck in our minds: she noticed that his back legs seemed cooler than the rest of his body. We knew to advise her to bring Templeton in right away.

We examined the 10-year-old cat and noticed that in addition to his hind leg coolness, his nails had a bluish tinge, and he had no pulse in the vessels of his back legs. We took an x-ray (radiograph) and found that he had an enlarged heart, probably caused by a condition called "dilated cardiomyopathy." The x-rays, EKG, ultrasound, and physical exam confirmed our suspicions about why Templeton's legs were so weak and cold. A blood clot had formed in the heart and was released into the aorta (the major artery running through the body). It traveled through Templeton's bloodstream until it reached the narrower arteries just above the hind legs (called the iliac arteries). There it blocked the blood flow to his legs, causing the problems. This condition is called a "saddle thrombus," also referred to as a "thromboembolism."

About Saddle Thrombi

Saddle thrombi get their name because the blood clot resides at the junction of the aorta and the arteries of the back leg (iliac arteries) and resembles a saddle. Since the iliac arteries supply blood to the back legs, the blood clot cuts off this circulation, and the rear muscles are no longer able to function.

A cat with a saddle thrombus experiences extreme discomfort as his legs are deprived of oxygen. The back legs are cold because of the dramatic decrease in circulation.

These blood clots are much more common in cats who have heart problems. In fact, this is often the first indication to an owner that their cat has heart disease.

Sometimes the blood clots totally block the arteries; sometimes there is only partial blockage. Partial blockages have a better long-term prognosis.

Illustration of saddle thrombus

We administered anticoagulants and pain relieving medications to Templeton and restored the blood flow in his back legs. We also treated the primary heart problem.

Even though he eventually recovered, he has not regained full use of his back legs and his owner had to get a ramp so he could get up onto his favorite spying spot.

Unfortunately, cats that develop one saddle thrombus are also more likely to develop future saddle thrombi. We are hoping the best for Templeton. Although he is on medication, unfortunately, there is no way to guarantee it from happening again.

The incidence of cardiomyopathies and therefore saddle thrombi has decreased dramatically in recent years. This is because research has indicated that taurine, an amino acid, helps keep hearts healthy. Today, almost all cat foods contain taurine.

Remember, weak or dragging hind legs is a veterinary emergency. This is one of those cases in which avoiding treatment can lead to permanent paralysis.

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