By Dr. Becker
Horner's syndrome is a neurological disorder of the eye and muscles of the face. It occurs when there is damage to the sympathetic nervous system that stimulates the eye on the affected side of the head.
The disorder is seen in both dogs and cats. Golden Retrievers and Cocker Spaniels seem to have a slightly higher risk than other breeds.
Symptoms of Horner's Syndrome
The onset of Horner's syndrome is often sudden and without warning. Signs include a drooping eyelid, pupil constriction, retraction of the eyeball into the head which gives it a sunken appearance, prolapse of the third eyelid giving it a red, raised appearance, and increased pinkness and warmth of the ear and nose on the affected side of the head.
Sometimes there is also excessive drooling or difficulty eating on the affected side.
Causes of Horner's Syndrome
The nerves that provide sympathetic control to the eyes travel a long path through an animal's body. They start in the brain stem, travel down the spinal cord through the neck and exit just inside the chest, where they form the cervical sympathetic trunk.
The cervical sympathetic trunk is a bundle of nerves that travels outside the spinal cord back up through the neck to the middle ear. These nerves then connect to new nerves just below the ear, and the new nerves continue to the eye.
If the sympathetic nervous system supplying the eyes is damaged or not functioning properly, the parasympathetic system takes over, and Horner's syndrome is the result.
As you can imagine, with such a long route to travel, there are several areas of the upper body where damage to these nerves can occur. Damage can be the result of blunt trauma or a bite wound, a tumor, intervertebral disc disease, a blood clot, a disease of the middle or inner ear, or a disease of the eye.
About half the cases of Horner's syndrome in dogs are idiopathic, meaning no cause can be found. In cats, there is almost always an identifiable cause. Sadly, the most common cause is trauma from being hit by a car.
Diagnosis and Treatment
Your veterinarian will ask for a detailed history of your pet's health, the onset and details of symptoms, and possible incidents or health problems that might have caused the condition.
A thorough physical exam will be performed, including an otoscopic exam of the ears, and a neurologic evaluation. Routine lab tests (complete blood count, blood chemistry profile, urinalysis) are usually performed to check for other possible diseases and infections.
X-rays can show brain and spinal cord lesions, and images of the skull can be helpful in evaluating ear problems, especially in cats. Often a CAT scan, MRI or ultrasound will be used as a diagnostic tool. In some cases, a sample of cerebrospinal fluid is taken to look for possible brain or spinal cord disease.
Determining which area of the sympathetic nervous system (the first or second nerve segment) can be very helpful in determining the nature of the damage and what additional diagnostic tests may be necessary.
Horner's syndrome itself doesn't require any specific treatment, however, your pet will need to be treated for the underlying cause of the condition. The treatment protocol will depend on the root cause.
If the condition is idiopathic, meaning no root cause can be identified, the best course of action is to allow the disorder to resolve on its own. This can take six to eight weeks. During this time, I recommend your pet receive acupuncture, as it can be very beneficial in reducing the intensity of the symptoms, and the duration of what can be a pretty frustrating nervous condition.