Lainie Kringen-Scholtz

Lainie Kringen-Scholtz

Neurology is a super complex and exciting area of study in veterinary medicine.

In this article, I am going to discuss one syndrome of the nervous system that I find particularly fascinating; Horner’s syndrome. I apologize in advance for all the parentheses. I’m a nerd and can’t help but use nerdy words.

What is Horner’s syndrome?

Whenever you see the word “syndrome” associated with a condition, it means that there are a group of clinical signs that consistently occur together. Thus, Horner’s syndrome is a condition that is characterized by its clinical signs.

These include miosis (constriction of the pupil), ptosis (drooping of the eyelid), enopthalmos (sinking in of the eye), prolapse of the nictitating membrane (third eyelid), and unilateral sweating (one sided).

What causes these clinical signs?

A variety of different conditions cause Horner’s syndrome. The one thing that is common between all the causes, is a lesion that involves the sympathetic (fight or flight) nervous system.

These lesions can be caused by head or neck trauma such as fractured bones, soft tissue injuries, or wounds. Irritation can be caused by perivascular (around the vein) administration of vitamin E/selenium, xylazine and phenylbutazone.

This is one example of why it is so important to know that you are administering these medications intravenously (in the vein). Local infections or cancer in the areas shown in the diagram can cause Horner’s syndrome.

Diseases of the guttural pouch (extension of the eustachian tube that is located under each ear) or brachial plexus (armpit) likewise may be the culprit.

How is Horner’s syndrome diagnosed?

Horner’s syndrome should be diagnosed by your veterinarian. It is fun practicing alternative medicine because cases like this often first seek chiropractic treatment. In the end, chiropractic treatment would just be a waste of money because the cause of Horner’s syndrome is not a vertebral subluxation, as described above.

Your veterinarian will perform one or more of the following: a physical and neurologic examination, X-rays, endoscopy of the guttural pouches, and/or ultrasonography.

What are the complications associated with Horner’s syndrome?

Because the horse may not be able to blink, ulceration of the cornea is a common complication.

The hair might be lost (alopecia) over the areas where the horse is sweating. The facial nerve may be damaged causing facial nerve paralysis in which the facial muscles do not function properly causing the eyelid and ear to droop on the affected side.

Athletic performance may be hindered if the nasal passage becomes obstructed from nasal mucosal edema (swelling inside the nose) or from laryngeal hemiplegia (roaring) secondary to Horner’s.

How is Horner’s syndrome treated?

Horner’s syndrome has to be treated based on the cause. If there is an infection in the guttural pouches, it needs to be lavaged out and treated. If it is due to a fracture, the fracture may need to be repaired. If there is a localized infection from a wound, antibiotics and wound management should be started. And so on and so forth.

What is the prognosis Horner’s syndrome?

The prognosis depends on the inciting cause. In one study, horses were typically affected for five months but ranged from 14 days to 15 months (Green et al. “Horner’s Syndrome in 10 Horses,” Canadian Veterinary Journal, Volume 33, May 1992).

Working closely with your veterinarian may be able to decrease the duration of Horner’s syndrome with the appropriate treatment.

Questions? Email Eric Knock, DVM, at

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