If your cat’s back legs suddenly collapse, drag, or stop holding its weight, call an emergency veterinary clinic now. The most time-critical cause is a saddle thrombus, a blood clot that can block blood flow to the hind limbs. Owners cannot reliably tell a clot from an injury or a nerve problem at home, so the cat needs a veterinary examination right away.
Tufts Cummings School of Veterinary Medicine states in its “Rear Limb Weakness” guidance: “The development of a clot is an emergency. Veterinary care should be sought immediately.” PDSA’s guidance on saddle thrombus (aortic thromboembolism) in cats says the condition is an emergency and that owners should contact a vet immediately when symptoms appear.
What the signs mean
Veterinarians describe reduced use of the back legs as hind-limb weakness. Partial loss of movement is called paresis, and complete loss of movement is called paralysis. Both are signs rather than diagnoses, so each one needs an examination to find its cause.
Treat any of the following as an emergency:
- A sudden inability to stand, or back legs that give way under the cat
- Dragging one or both hind legs, or a cat that will not use them
- Weakness in one or both hind legs, even when the cat can still bear some weight
- Pain, crying, or vocalizing, including resistance to having the legs touched
- Cool hind legs or paws
- Labored or rapid breathing, or coughing
Each of these matters, but none settles the cause on its own. The table below explains what each clue may suggest and where it stops being useful.
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Causes
Feline aortic thromboembolism (saddle thrombus)
A thrombus is a blood clot. In feline aortic thromboembolism (ATE), often called a saddle thrombus, a clot can travel from the heart and lodge where the aorta divides toward the hind limbs. The clot blocks arterial blood flow to one or both back legs. The event can appear abruptly. Because the blockage can be partial, the cat may show weakness rather than complete paralysis.
Heart disease is the condition most closely associated with ATE, and some affected cats also show signs of congestive heart failure, such as breathing difficulty. For background on the heart condition itself, see Tufts Cummings School of Veterinary Medicine’s “Heart Disease – Cats” guidance.
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A cat that looks otherwise healthy can still have ATE, and no owner can reliably tell a clot from an injury by looking at the legs.
Other possible causes
Hind-leg weakness can also result from trauma, neurologic or spinal problems, and other circulatory or systemic illnesses. Signs seen at home cannot reliably rank these possibilities. The veterinary examination decides which causes are pursued.
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Clues and what they cannot tell you
| Clue | What it may point toward | What it cannot tell you |
|---|---|---|
| Sudden onset | ATE can appear abruptly; injuries can also be sudden | Onset alone does not identify a clot or any other cause |
| One leg or both legs | ATE can affect one or both hind legs | The pattern alone does not separate ATE from injury or a neurologic problem |
| Pain or crying | A concerning sign that the cat needs urgent assessment | Its presence does not confirm a clot, and its absence does not rule one out |
| Cool hind limbs | Suggests reduced circulation to the legs | Coolness does not show what is blocking circulation |
| Breathing difficulty or known heart disease | Links to heart disease and congestive heart failure, the main ATE association | Does not confirm either a clot or heart disease by itself |
| Known trauma | Makes an injury a possibility to raise with the veterinarian | Does not exclude a clot |
What to do now
- Call an emergency veterinary clinic now and follow its instructions.
- Tell the staff when the problem began, whether one or both hind legs are affected, whether the cat seems painful or is crying, whether the legs feel cool, and whether there is any breathing difficulty or known heart condition.
- Keep the cat still and calm. Do not massage, stretch, or warm a painful or poorly circulated leg as a substitute for care.
- Transport the cat as the clinic directs. A secure carrier can make the trip safer for the cat and the person carrying it, but it is only a way to move the cat. It should not delay the call or the trip.
- Give no medication. Many human pain medicines are dangerous to cats, so give nothing unless a veterinarian specifically directs it.
No home treatment replaces veterinary care for this condition.
What the veterinary workup involves
The veterinarian begins with the history and a physical examination of limb function, pain, circulation to the hind legs, and neurologic function. The examination also looks for possible heart or lung involvement. Depending on the findings, testing may include:
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- Blood tests
- Chest radiographs (X-rays)
- Echocardiography, an ultrasound examination of the heart
- Other tests to look for heart disease, heart failure, or the alternative causes listed above
ATE may be suspected from its characteristic presentation. Confirming it, choosing the tests, and deciding when to stabilize the cat are decided case by case.
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Hospital care
The veterinary team sets the plan for each cat. It may include hospitalization, pain control, supportive care, treatment intended to reduce further clotting, and evaluation or management of any underlying heart disease. Some cats need substantial nursing care during recovery.
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What the recovery figures mean
The Merck Veterinary Manual’s entry “Blood Clots and Aneurysms in Cats” reports that more than 50% of cats surviving a cardioembolic event regain some hind-limb function over 4–6 weeks with conservative medical therapy. This is a group-level figure, not a prediction for an individual cat. The Merck page does not state a publication year.
Tufts Cummings School of Veterinary Medicine notes that some cats regain function. It also describes a 24–48 hour treatment trial as reasonable in some cases, in its clinical view. That is a judgment for the veterinary team while the cat is under care. It is not a reason to watch the cat at home.
No one can promise that a clot will dissolve, that the legs will recover, or that a given treatment will work. Outcome depends on the individual cat and how much of its body is affected.
Quick Recap
Sources
- Tufts Cummings School of Veterinary Medicine, “Rear Limb Weakness”
- PDSA, “Saddle thrombus (aortic thromboembolism) in cats”
- Merck Veterinary Manual, “Blood Clots and Aneurysms in Cats”
- Tufts Cummings School of Veterinary Medicine, “Heart Disease – Cats”
- Melissa Boldan, DVM, “Saddle Thrombus in Cats: Causes, Symptoms, and How To Help Your Cat,” PetMD, July 22, 2024
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