What is Horner’s Syndrome, and what causes it?

Horner’s Syndrome is a group of signs that occurs when specific muscles of the face lose their stimulation by certain nerves, specifically the sympathetic nerves. It is caused by some type of injury to, or lesion of, the nerves. The injury may occur at the level of the brain, upper spinal cord, or between the spinal cord and the face. In the dog, the most common causes are:{{more}}

o Idiopathic (cause unknown)

o Car accidents with trauma to the head, neck, or chest

o Bite wounds

o Intervertebral (IV) disc disease in the neck area

o Infections of the middle ear

o Disease of the orbit (area behind the eye)

o Cancer involving the brain or chest

o As a result of a treatment (e.g. ear cleaning) or medication

For an unknown reason, Horner’s Syndrome appears to be more common in Golden Retrievers. Approximately 40-50 per cent of the cases of Horner’s Syndrome in dogs are idiopathic.

What are the signs of Horner’s Syndrome?

The classic signs of Horner’s Syndrome occur on the same side of the face as the injury, and include:

1. Small pupil size (miosis)

2. Protrusion of the third eyelid

3. Drooping of the upper eyelid (ptosis)

4. Sunken appearance to the eye (enophthalmos)

5. Dilation of blood vessels on affected side of the face, which makes the area feel warmer to the touch.

How is Horner’s Syndrome diagnosed?

Horner’s Syndrome is diagnosed by the presence of the signs listed above, as well as more specific diagnostic methods. What is more difficult is the diagnosis of the cause of the condition.

How is Horner’s Syndrome treated?

Depending upon the location of the injury, phenylephrine eye drops are administered to relieve the clinical signs. The underlying cause, such as a bite wound or middle ear infection, should be treated. In cases of idiopathic Horner’s Syndrome, the condition often resolves after six to eight weeks. Horner’s Syndrome caused by injuries to nerves outside of the brain and spinal cord generally have a better prognosis.

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