My dog was diagnosed with Horner's syndrome. What exactly is it and what treatment is available?
Horner's syndrome is characterized by enophthalmos (retraction of the eyeball), ptosis (drooping of the upper eyelid) and a narrowed pupil. The third eyelid may protrude and the opening of the eye may be narrowed. It occurs when there is a disruption of the nerve path travelling from the hypothalamus in the brain, down the spinal cord and back to the eyes. Specifically, this nerve pathway innervates the muscles of the third eyelid (nictitans), Muller's muscle (the smooth muscle of the eyelids), the pupil, and the smooth muscle about the eye.
Trauma to the neck or anywhere along the nerve path can cause Horner's syndrome. Infection, inflammatory diseases, nasopharyngeal polyp, neoplasia (tumors and other growths), infarction (blockage) of arterial circulation to certain parts of the nervous system and idiopathic etiology (unknown cause) may result in Horner's syndrome as well. Even blood collection from the neck or placement of a jugular catheter can cause Horner's syndrome on that side.
The nerve pathway involved in Horner's syndrome is part of the autonomic nervous system, which regulates smooth muscle function among other things. Autonomic nerves consist of nerve cells that are either preganglionic or postganglionic. This anatomic distinction is important in the diagnosis, treatment, and prognosis of Horner's syndrome.
The diagnosis of Horner's syndrome is based on physical exam findings. The veterinarian can determine whether the nerve disruption has occurred in a preganglionic or a postganglionic nerve fiber with the use of adrenaline eye drops. Generally, if a postganglionic fiber is affected, Horner's syndrome goes away in weeks to months, depending on the underlying cause. The prognosis for recovery for postganglionic problems is usually good.
If the problem involves a preganglionic fiber, additional diagnostics will likely be needed, unless there is a known history of trauma to the neck or front legs. A neurological exam, radiographs (x-rays), bloodwork, and in some cases, CAT or MRI scans may be required to diagnose the underlying problem to enable appropriate treatment. The prognosis for preganglionic problems depends on the underling cause.
Treatment may involve surgery or the administration of antibiotics, anti-inflammatory agents, or other drugs, depending upon what caused the symptoms of Horner's syndrome.
Please follow your veterinarian's instructions for caring for your dog. Continuing communication with your veterinarian about your dog's progress and status is an important part of your pet's care. Consultation with a veterinary ophthalmologist or neurologist may be advised.
01/29/09
