The cause of this disease is unknown. It can be temporary or progressive. It may be traumatic in origin, but some think there are other causes, such as viral or bacterial. It is uncommon and usually affects adult horses. There is a unilateral paralysis of the facial nerve, causing the ear, the eyelid, and the muzzle of one side of the face to lose its tone. See the images below. Eyelid paralysis may cause a secondary corneal ulcer; pay attention to this.

It can be associated with temporohyoid osteoarthropathy (THO), joint arthritis between two hyoid bones, a basket of bones surrounding the throat and attached to the tongue and skull. The question is whether the neuropathy of the head is from a primary insult or secondary to THO.

Treatment of THO is surgical, with the removal of the affected joint or joints providing relief from pain. In floating teeth, some of these horses object to any physical movement of the tongue, requiring pain medication to perform the procedure. In my experience, it does not affect the wearing of the teeth. Other signs include difficulty chewing (this may be from unrelated tooth issues), head shaking, and other vague signs of something bothering the horse in the head area. Diagnosis requires imaging (X-rays, CT, MRI).

Horses affected by Horner’s need to see a veterinarian quickly. Treatment may include anti-inflammatories or, if indicated, antibiotics. Surgery has a good outcome, but due to several sensitive structures, it has risks. 

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