This is characterized by the passing of a blood clot (embolus) from the left side of the heart into the general circulation, where it becomes lodged in an artery. The resulting obstruction to the flow of blood leads to clotting of the artery (thrombosis).
The most common site for blockage is the point at which the abdominal aorta branches into the main arteries that supply the rear legs. Arteries elsewhere in the body can be affected, particularly in the kidneys. Diagnosis of the rear limb problem can be based on signs such as rear limb paralysis, swollen muscles, the absence of a pulse in the groin, and blue nails due to cyanosis. If the renal arteries are blocked, acute kidney failure may result. If a cerebral artery is blocked, seizures may occur. Cats with thrombi can be in quite serious pain.
The most common behavior problem reported by pet parents of cats is inappropriate elimination. It’s estimated that 10% of all cats will eliminate outside their litter box at some point in their lives. Quite a few of these cats have issues with some characteristic of their litter box (please see our article on Litter Box Problems for more information on litter box problems), but approximately 30% don’t have litter box problems at all. These cats are urine marking, and urine marking isn’t a litter...
Formation of a blood clot in the heart and subsequent arterial thromboembolism occurs in about half of all cats suffering from cardiomyopathy. It may be the first indication of heart disease. Suspect this possibility if your cat experiences the sudden onset of weakness in the rear legs. Look for cold legs, bluish skin, and faint or absent pulses in the groin. One leg may be more severely blocked than the other. The colder leg with the weaker pulse is the more severely affected. Ultrasound can be very useful in localizing all potential areas of thrombosis.
Treatment: This depends on the severity of the blockage. Your veterinarian can prescribe medications to try to dissolve the clot. Heparin seems to be the most useful drug for this condition. Aspirin may also be used, and a new product called Fragmin, which is a molecular weight heparin (a version of heparin that is smaller in size - molecular weight - than standard heparin), may also be useful, but it is very expensive and is not approved for use in cats at this time. Clopidogrel is currently being tested at Purdue University to see if it will reduce the recurrence rate of thromboembolism. Surgery has not been found to have a high success rate.