Understanding Horner’s syndrome in dogs: Causes, signs, treatment

Horner’s syndrome in dogs is a neurological condition caused by damage to the sympathetic nervous system that controls nerve supply to the eyes and facial muscles on one side of the face. This disorder leads to distinctive eye-related signs and changes in appearance, which can be alarming for owners.

While it can develop in dogs of any breed and age, Horner’s syndrome is most frequently diagnosed in Golden Retriever puppies, making owners of this breed particularly aware of its symptoms and care.

In this article, we will explore Horner’s syndrome in detail, including its causes, symptoms, diagnosis, and treatment, providing practical guidance for responsible dog owners.

What is Horner’s syndrome in dogs?

Horner’s syndrome results from damage or disruption to the sympathetic nerve pathway that extends from the brain, through the neck, and into the eye and surrounding face muscles. This pathway comprises three neuron groups:

• First-order neurons: from the brain to the spinal cord
• Second-order neurons: from the spinal cord to the cranial cervical ganglion
• Third-order neurons: from the cranial cervical ganglion to the eye and facial muscles

When this nerve supply is impaired, the affected eye and side of the face cannot function normally, leading to characteristic signs such as constricted pupils and drooping eyelids due to the parasympathetic nervous system dominating.

What causes Horner’s syndrome?

The causes are varied and sometimes unknown. Around half of cases are idiopathic, where no clear cause is found. When a cause is identifiable, common factors include:

• Trauma to the head, neck, or spinal cord (e.g., accidents, bites)
• Ear infections or damage during ear cleaning impacting nearby nerve pathways
• Tumours or lesions in the brain, spinal cord or nerves supplying the face
• Intervertebral disc disease or spinal degeneration
• High-impact activities causing spine injuries or misalignments

Which dogs are at risk?

Horner’s syndrome can affect any breed, age, or sex. However, it is more commonly seen in certain breeds, notably:

• Golden Retrievers
• Labrador Retrievers
• Shetland Sheepdogs
• Collies
• Doberman Pinschers
• Weimaraners

Middle-aged dogs often experience idiopathic Horner’s syndrome, but puppies and senior dogs are also susceptible.

Recognising the symptoms

Signs usually appear suddenly and affect one eye, though both may be involved if the brain itself is impacted. Key symptoms include:

• Constricted pupil (miosis) on the affected side
• Drooping upper eyelid (ptosis) causing a tired appearance
• Elevated and visible third eyelid (nictitating membrane) over the eye
• Sunken or retracted eyeball
• Increased warmth and redness on the affected side of the face, nose, or ear

The syndrome is generally not painful, but the visual change can affect your dog’s vision and appearance, prompting prompt veterinary assessment.

How is Horner’s syndrome diagnosed?

A vet diagnoses Horner’s syndrome by examining the classic signs and may use various diagnostic tools to pinpoint the underlying cause, including:

• Thorough physical, neurological, and ophthalmic examinations
• Ear examinations and cultures if infections are suspected
• Imaging such as MRI, CT scans, or chest X-rays to identify tumours or spinal problems
• Pharmacologic tests like pupil response to phenylephrine to localise nerve damage

Early diagnosis helps guide targeted treatment of underlying causes and management of symptoms.

What treatment options are available?

Treatment focuses on addressing the cause of the nerve damage, if known. For idiopathic cases, the condition often improves spontaneously within a few weeks to two months.

Typical approaches include:

• Antibiotics or anti-inflammatory medications for infections
• Managing or surgically addressing tumours or spinal issues
• Supportive care, including monitoring vision and comfort

It’s important to seek veterinary advice swiftly if signs of Horner’s syndrome appear, to ensure accurate diagnosis and appropriate care.

Frequently asked question: Can Horner’s syndrome recur or become chronic?

Quick Answer: Horner’s syndrome can recur if the underlying cause persists or if the nerve damage is irreversible, although some dogs experience complete and lasting recovery after initial treatment.

Dogs with idiopathic Horner’s syndrome often recover fully and do not have ongoing issues. However, recurrence may happen if the condition results from progressive diseases like tumours or chronic infections that damage nerves repeatedly. Regular veterinary monitoring is advised to manage and detect any recurrence early to maintain your dog’s quality of life.

Responsible dog owners should understand that prompt veterinary care, including diagnostics, can help detect treatable causes and prevent complications or chronic problems.

Horner’s syndrome is a distinctive neurological condition affecting the sympathetic nerves of the eye and face in dogs. Early recognition and veterinary evaluation are crucial for managing underlying causes and helping your dog recover gracefully.