Aortic Thromboembolism In Cats
By Rachele Baker, DVM – Dot, a female black cat, was brought into the veterinary hospital where I was working because her left rear leg had suddenly become paralyzed earlier that day. Her owners had noticed that Dot had been favoring her left rear leg for at least four or five days. Dot had been vocalizing and acting like she was in pain for the first day or two after she started favoring her left rear leg but had not seemed to be in pain since then.
When I examined Dot, she was unable to use her left rear leg. Her left rear leg was outstretched and she dragged it behind her when she walked. I was able to flex and extend all of the joints in her left rear leg and the joints had full range of motion. I did not palpate any swelling or obvious fractures in her leg. I could not find any injuries. I palpated her spine to see if there was any pain in her spine but she did not give me any pain response during palpation of her spine.
When I pinched the skin between her toes on her left rear leg, there was no normal reflex withdrawal of the leg. When I pinched the skin between the toes of her right rear leg, that leg withdrew normally. I palpated both rear legs at the same time to see if there was any difference in the warmth of her rear legs but I was not able to appreciate any difference in body temperature between her two rear legs. Her rear leg paw pads were black in color and I was not able to discern any color difference between the paw pads on her rear legs.
I did not auscult a heart murmur or any problems with her lungs. She did not have any enlarged lymph nodes. Her abdomen palpated normally. She was about 8-10% dehydrated. When I advised Dot’s owner of this, he told me that since Dot had been having trouble getting around due to problems with her left rear leg, she had not been drinking as much as she normally would.
I told Dot’s owners that there were several things that could be causing the paralysis of Dot’s left rear leg and that we would need to perform some diagnostics to enable me to reach a diagnosis. I advised Dot’s owners that the possibilities included: 1) a blood clot obstructing blood flow to her left rear leg; 2) herniation of one of the intervertebral discs in her spine resulting in compression of her spinal cord; or 3) trauma to her spine or leg.
Dot is a diabetic cat and she normally receives insulin twice a day. Since she had not been eating well since the problems began with her leg, her owners had not given her insulin on a couple of occasions during the past week. I recommended that we begin our diagnostics by performing bloodwork, urinalysis, x-rays of her spine, and x-rays of her rear legs.
X-rays of Dot’s spine did not show any evidence of intervertebral disc herniation or trauma. X-rays of Dot’s back legs did not show any evidence of any bony lesions or fractures.
When I palpated the femoral artery in Dot’s right rear leg, I could detect a pulse. When I palpated the femoral artery in Dot’s left rear leg, I could not detect any pulse. At this point, I was nearly positive that Dot had a blood clot obstructing blood flow to her left rear leg. To confirm this, I cut one of the toenails on Dot’s left rear leg down to the “quick” (the blood vessel in the toenail) and no blood came out. If you have ever accidentally cut a cat’s toenail too short (down to the “quick”), you will have observed that the toenail bled a lot. So now I knew that Dot had a condition called “aortic thromboembolism.”
“Aortic thromboembolism” is a blood clot in the caudal portion of the aorta (the largest blood vessel in the body). The blood clot obstructs blood flow to the back legs. The word “thromboembolism” is comprised of the terms “thrombo” (from the word “thrombus” which means “blood clot”) and “embolism” which means “obstruction of a blood vessel.” The blood clot originates in the heart and then travels through the aorta and may become lodged at the caudal aspect of the aorta where the aorta branches into the iliac arteries. This will result in obstruction of blood flow to both back legs. The blood clot may also lodge in one of the iliac arteries and obstruct blood flow to only one of the back legs. A large majority of cats who develop aortic thromboembolism have heart disease and it is common that sudden paralysis of one or both rear legs is the first sign of heart disease in those cats.
The clinical signs of aortic thromboembolism in a cat include a sudden onset of pain together with partial or complete paralysis of one or both rear legs, decreased or absent femoral pulses in one or both rear legs, and pale paw pads in one or both rear legs. The pain the cat experiences will subside in a day or two as the sensation to the affected leg is lost. Notice in the photo that the paw pads on the right are pale in comparison to the paw pads on the left. This is a photo of a cat with aortic thromboembolism that caused a blockage of blood flow to one of the cat’s rear legs.
Once a clot has lodged in the caudal aorta or an iliac artery, the cat’s body will begin to work to break down the clot. The cat’s body may succeed in dissolving the clot either partially or completely and then the cat may regain partial or total function of the hind limb involved. Recovery can take anywhere from one to six weeks. Some cats are not able to break down the clot and their hind limbs may remain permanently paralyzed. After recovery, it is common for aortic thromboembolism to recur.
Treatment consists of restricting the cat’s activity by confinement to a small room or cage. If the cat is brought to the veterinary hospital at the onset of paralysis and is in pain, then pain medications will be administered. Heparin and aspirin have been used to try to prevent new clots from forming but neither has proven effective at preventing recurrence of thromboembolism. Neither heparin nor aspirin will dissolve an existing blood clot. If the cat is in heart failure, heart medications will be prescribed.
A recent study showed that Plavix (clopidogrel) was more effective in preventing recurrence of aortic thromboembolism than aspirin and that cats that had experienced aortic thromboembolism that were treated with Plavix had a longer survival time than those treated with aspirin.
I recommended to Dot’s owner that we take x-rays of Dot’s chest to see if her heart was enlarged and that we give Dot some subcutaneous fluids to rehydrate her. I also recommended that we start Dot on Plavix. Dot’s owner agreed to allow us to give Dot subcutaneous fluids but decided that she wanted to wait to get the results of the bloodwork before we proceeded with any further diagnostics or treatment. She elected to take Dot home and keep Dot confined to a small room while she was recovering.