Horner’s Syndrome in Cats
Horner’s syndrome in cats. Maybe you’ve heard of it, maybe you haven’t. Maybe you’ve been wondering what it is, how to tell if your cat has it, and what to do about it. If so, you’ve come to the right place.
Not many cats will experience Horner’s syndrome. It involves a very specific set of symptoms in the eye due to a variety of medical conditions, injuries, or surgeries. Many cats will eventually resolve the syndrome and have a good quality of life, but it’s normal to wonder: what is Horner’s syndrome? And what causes it?
What Is Horner’s Syndrome?
First things first. Horner’s syndrome is when an animal has distinct changes in the eye, and it typically occurs in only one eye. While it is a rare condition, it affects many species, including humans, dogs, and cats.
A cat has Horner’s syndrome when they have at least three out of these four signs:
- Constricted, small pupil, also known as miosis
- Droopy upper eyelid, also known as ptosis
- Sunken eye, also known as enophthalmos
- Third eyelid elevation (pink flesh that comes from the inner corner of the eye but stays up instead of moving up and down when blinking)
Francois Pourfour du Petit wrote about this syndrome in 1727 after experimenting with the nerves running along the outside of the chest in animals. In future centuries, physicians attempted to understand the syndrome further, and a thorough explanation of what causes it was given by ophthalmologist Johann Friedrich Horner in the mid-19th century.
What Causes Horner’s Syndrome in Cats?
The cause of Horner’s syndrome is the disruption of the sympathetic nerves to the eye. The sympathetic nervous system maintains the body’s involuntary processes, or things that an animal cannot control. For example, the pupil dilates in dim light and gets smaller in bright light. A person or animal does not think about this process – it just happens.
The sympathetic nerves that reach many components of the eye travel from the brain stem down through both the neck and chest spinal cords. The nerves then leave the spinal cords to go back toward the head through the chest, into the neck, past the base of the ear, and up to the structures of the eye.
Causes of Horner’s syndrome involve parts of the body in which the sympathetic nerves pass:
- Inflammatory conditions of the brain, especially the brainstem
- Trauma to the head, neck, chest, or spinal cord near those areas
- Issues inside the chest such as tumors or blood
- Ear issues such as middle ear infections
- Cancer in the neck, spinal cord, nerves under the armpit (brachial plexus), or lungs
- Medical care such as surgery of the jaw, ear, or neck
- Vascular (blood vessel) disease such as blood clots (rare)
- Inflammation of nerves (also rare)
About 40 percent of all cases of Horner’s syndrome in cats are considered idiopathic, meaning a cause cannot be identified.
Horner’s Syndrome Symptoms in Cats
As previously mentioned, cats with Horner’s syndrome must have three of the four signs outlined above in at least one eye.
Since most cases have an underlying cause, other symptoms may include:
- Inability of blood vessels to constrict locally, causing redness in the eye
- Neurologic issues such as changes in behavior, limb weakness, or stumbling
- Pain, especially of the front legs or head/neck
- Decreased ability to breathe well (i.e. fast breathing rate)
- Regurgitation (passive ejection of food from the gastrointestinal system) or trouble eating
- Head-shaking
- Debris or redness in the ears
Diagnosing Cats with Horner’s Syndrome
Cats are diagnosed with Horner’s syndrome through physical examination by a veterinarian; no special tests are needed. To find the cause of Horner’s syndrome, a more in-depth physical examination, thorough history from pet parents, and testing are all required.
During the physical examination, your veterinarian will look deep into your cat’s ear canals to see the eardrum and attempt to look for signs of middle ear disease. Evaluation of your cat’s gait (walk) and a more thorough neurologic examination are necessary.
When it comes to finding the actual cause, a complete understanding of your cat’s recent health and activities is needed to solve the puzzle that is Horner’s syndrome. Consider if there is any chance for trauma – did your cat leave the house for a little while? Did you notice any wounds or limping? Has there been any head-shaking? Has he undergone surgery recently?
Testing will be done to find the cause of cat Horner’s syndrome. X-rays are important to look for issues in the chest, like tumors or evidence of trauma. Sometimes x-rays are done on the skull to look for evidence of middle ear disease. Advanced imaging may be recommended via a specialist, like a CT scan of the skull and chest, or an MRI of the brain, spinal cord, and other nerves. In rare cases, if the cause is in the brain, a spinal tap to look at the fluid surrounding the spinal cord and brain may be performed.
When finding the exact cause proves to be challenging, a test can be performed at the veterinary clinic using an eye medication called phenylephrine at a very low concentration that stimulates the sympathetic response. When the medication is applied, it should dilate the pupil after 30 minutes – but only in cats with damage to the sympathetic nerves leading to the eye at the level of the skull. If the nerves were damaged elsewhere, such as the spinal cord or chest, the test won’t work. In short, this test determines where the damage is to identify the cause.
Keep in mind that nearly half of cats never have a cause identified, but it’s important to run tests to look for a cause – especially if your cat has symptoms other than the signs in the eye itself.
Horner’s Syndrome Treatments
There are currently no treatments for Horner’s syndrome. If there is an underlying cause, the cause should be treated, and Horner’s syndrome may eventually go away.
In some cats, Horner’s syndrome never goes away or only does so partially. If cat Horner’s syndrome was caused by inner ear surgery, about 25 percent of felines will have it permanently. If no cause was identified, Horner’s syndrome usually resolves on its own, but it takes at least two months.
How to Prevent Horner’s Syndrome in Cats
While some of the causes of Horner’s syndrome in cats are preventable, most are not. Avoiding trauma is best done by keeping your cat indoors and away from situations in which they could become hurt, like not letting them onto a balcony where they could fall or jump.
If you notice debris or redness in your cat’s ears, scratching at their ears, or head-shaking, bring them to your veterinarian as soon as possible to treat the ear infection before it gets worse and causes Horner’s syndrome.
If you notice any changes in your cat’s behavior, such as how they walk, their appetite, or their activity level, bring them to your veterinarian for a full evaluation. A medical condition could be found before it results in Horner’s syndrome.
