Horner's Syndrome in Dogs

Horner's syndrome is a disorder of neurological origin that we'll be able to spot as a change in one or both of our dog's eyes. There are different causes that can trigger it, and they vary in severity.

Diagnosing Horner's is simple, since we can see the eye looks different, but it's not easy to discover the cause. That's why specific tests are used. For some dogs, the damage is irreversible, while others recover spontaneously.

What Is Horner's Syndrome?

Horner's syndrome is a neuro-ophthalmological disorder caused by a failure in the contraction of facial muscles due to a communication error in the nervous system. This will affect the eye. The syndrome is unilateral when it affects only one eye, or bilateral, if both eyes are damaged.

Which Dogs Does Horner's Syndrome Affect?

Horner's syndrome can be identified in any dog, but it's more common in adults. Some breeds have also been noted as more predisposed to it, such as the Golden Retriever.

What Causes Horner's Syndrome?

Behind the appearance of this syndrome, we can find trauma, a bite, otitis, or a tumor. But there are so many possible causes that, sometimes, one can't be determined. In this case, it would be called idiopathic Horner's syndrome, meaning unknown.

Symptoms of Horner's Syndrome

A dog with Horner's syndrome will show the following symptoms:

• Ptosis, or drooping of the upper eyelid.
• Miosis, meaning the pupil stays permanently constricted.
• The third eyelid, also called the nictitating membrane, prolapses, covering the eye to a greater or lesser degree.
• Enophthalmos, which we'll perceive as if the eye were smaller and had sunk into the socket.
• Redness of the eye and conjunctiva.

How Is Horner's Syndrome Diagnosed?

This disorder shows easily recognizable symptoms. The changes at the eye level can be directly noticed by owners. As soon as they're detected or suspected, we need to see the vet. With this clinical picture, there's usually no doubt it's Horner's.

But the problem, in this case, is discovering what triggered the syndrome. In addition, these symptoms are similar to those that can appear in other diseases, such as uveitis, which is eye inflammation. The vet will need to perform what's called a differential diagnosis to find the cause.

For this, a thorough neurological and ophthalmological exam is used. X-rays, ultrasounds, CT scans, or MRI are also considered. These last tests aren't always available or accessible.

Treatment for Horner's Syndrome

This will depend on what caused it. Although it's not always possible to identify it, it's essential to follow a good diagnostic protocol. For example, if the cause is something straightforward like middle ear otitis, treatment would involve treating the infection.

Prognosis for Horner's Syndrome

This will also depend on what triggered it. For example, if it's a tumor, it will be unfavorable. For other cases, there's no fixed rule. In some dogs, Horner's syndrome resolves spontaneously within a few months.

And this happens even without any treatment being given. But the opposite can also happen — meaning, for some dogs, this disorder will be irreversible to a greater or lesser degree.

Can Horner's Syndrome Be Prevented?

It's not possible to prevent every circumstance that can trigger Horner's syndrome, but some of them can be. To achieve this, these are the recommendations we should follow:

• Take care of the ears to prevent otitis from appearing, and see the vet at the first sign of infection, such as swelling of the ear flap or foul-smelling discharge.
• Shaking the head frequently, scratching against objects, or rubbing the ears with the paws are other signs that can point to an ear infection and require a vet check-up.
• If we want to clean our dog's ears, we should follow the vet's recommendations, never use cotton swabs, and never pluck the hairs found at the start of the ear canal. A mistake in cleaning can trigger Horner's.
• Watch out if we let our dog approach unfamiliar or aggressive animals. A fight, bites, or violent shaking can cause the syndrome.
• Keep our dog in a safe environment that prevents falls from great heights, escapes that could lead to attacks or being hit by a car, etc.
• For safety, it's recommended that walks, except in areas designated for dogs, be done on a leash to prevent escapes or conflicts.

Bibliography Carlson and Giffin (2002): Manual práctico de veterinaria canina. Madrid: Editorial el Drac. Poci Palumbo Antunes and Secorun Borges (2011): Síndrome de Horner en perros y gatos. Vet. e Zootec. 18 (3), 339-346.