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Horner's Syndrome

General Information

Horner's syndrome is a group of signs that indicate something is wrong along a certain nerve pathway inside the body.

The autonomic nervous system controls involuntary responses that aid the body in emergencies and maintain the normal internal state of the body. One subdivision of the autonomic nervous system is the sympathetic nervous system.

Diseases, tumors, degeneration and injuries along any portion of the sympathetic pathways may present certain recognizable signs, sometimes referred to as syndromes. One such collection of signs is called Horner's syndrome, and includes drooping of the upper eyelid, a small pupil, partial elevation of the third eyelid, and slight retraction of the eyeball within the socket.

Important Points in Treatment

1. The exact cause of Horner's syndrome is often very difficult to find, and sometimes the syndrome will simply disappear over an extended period. Occasionally it will remain with no apparent harm to the patient.

2. Since the syndrome may indicate serious disease, causes should be investigated.


Notify the Doctor if Any of the Following Occur:

* You note any changes in your pet.

* You cannot give the prescribed medication.

Question and Answer

What is Horner's syndrome?

Horner's syndrome refers to a set of changes that occur in the eye and surrounding tissues. The changes occur when the eye is deprived of its sympathetic nerve supply. They include a sunken eyeball, drooping of the upper eyelid, protrusion of the third eyelid, and a small or constricted pupil.

What causes Horner's syndrome?

Horner's syndrome is caused by a variety of lesions affecting the brain, spinal cord, middle ear, or the area behind the eyeball. A lesion is a broad term for abnormal changes in an organ due to injury or disease, especially if that change is well defined (such as a tumor). The locations of and types of lesions resulting in Horner's syndrome include:

In the brain:

In the spinal cord:


In the middle ear:

Behind the eyeball:

Many animals may have Horner's syndrome with no identifiable cause. These cases are considered to be "idiopathic."

What are the signs of Horner's syndrome?

Signs of Horner's syndrome include a backward displacement of the eyeball into the bony orbit (sunken eyeball), drooping of the upper eyelid, a protruding third eyelid, small or constricted pupil, and mildly bloodshot eyes. Other signs related to the cause of the Horner's syndrome might occur, depending on the location of the lesion. Some pets will have signs involving the central nervous system. The animal may have altered mental status, difficulty walking, paralysis, paresis (muscular weakness), and facial nerve paralysis.

How is Horner's syndrome diagnosed?

Horner's syndrome is diagnosed through physical examination. The veterinarian will examine the pet's ear to determine if an ear infection may be causing the Horner's syndrome. The veterinarian will do a thorough neurological examination (examination of the nervous system) and ophthalmologic examination (examination of the eye).

Imaging techniques such as radiographs (X-rays), magnetic resonance imaging (MRI), and computed tomography (CT) scans of the head, spine, and chest may be used to identify lesions that could cause Horner's syndrome. Skull radiographs may reveal middle ear problems. Radiographs of the spine may reveal spinal cord lesions. Radiographs of the chest may reveal trauma or tumors. Myelograms (special contrast X-rays) may be needed to identify lesions in the spinal cord. An ultrasound examination of the eye orbit may be needed to locate the offending lesion if it is located behind the eyeball. Other diagnostic tests may reveal lesions located in the brain stem, behind the eye, or in the middle ear. A spinal tap to collect cerebrospinal fluid may be needed to investigate spinal cord or brain disease.

How is Horner's syndrome treated?

Treatment of Horner's syndrome depends entirely on the underlying disease. No treatment is available for cases in which no cause is found (that is, idiopathic Horner's syndrome); however, some of these animals will recover partially or completely over several months.

What is the prognosis for animals with Horner's syndrome?

The prognosis (outcome) for animals with Horner's syndrome is variable. The outcome depends on the severity of the underlying cause. If the syndrome is idiopathic (no cause found), partial or complete recovery can be expected, but can take up to 4 months.

The information on this page was obtained from the site www.vetmedcenter.com