Horner's Syndrome in Cats

This occurrence is referred to as “Horner’s Syndrome”. It is a neurological disorder that is common in cats and often shows as abnormal eye and facial muscle positioning. The syndrome is usually unilateral, affecting only one side of the face. Damage to the sympathetic nerve path is classified into three areas. A first order injury is called a central lesion, where damage has occurred somewhere from the brainstem to the spinal cord. The second location differentiation is called a preganglionic lesion, referring to damage anywhere between the spinal cord and the superior cervical ganglion synapse (located near the mandible). A third order, or postganglionic lesion is found between the superior cervical ganglion synapse and the ocular nerves.

The autonomic nervous system of a cat is composed of two parts; the sympathetic and parasympathetic nervous systems. The sympathetic nervous system controls automatic or involuntary responses to fight or flight instincts. This involves pupil dilation, blinking, muscle tone and heart rate. The sympathetic nerve pathway is long, ranging from the brain to the chest. Damage to these nerves anywhere along the pathway can lead to the parasympathetic nervous system taking over the normal functions of the sympathetic nervous system. 

Most of the visible signs of Horner’s Syndrome involve the cat’s eyes. Other symptoms may be present depending on the underlying cause of the syndrome. Signs to watch for are as follows:

• Ptosis (drooping eyelid)
• Anisocoria (unequal pupil size)
• Conjunctival hyperemia (protruding third eyelid)
• Narrowing of the eye opening
• Sunken eye appearance
• Warmth and redness around eye and ear on affected side
• Drooling
• Head tilt
• Stumbling

The most common cause of Horner’s Syndrome is trauma from serious injury of the head, neck or spinal cord. Some instances of Horner’s Syndrome are idiopathic, carrying no obvious reason for nerve issues. Possible causes include.

• Car accident
• Bite wound
• Benign or malignant tumors in the chest, neck, brain or spinal cord
• Retrobulbar (behind the eye) disease
• Middle ear issues
• Intervertebral disc disease
• Blood clots

To diagnose your cat, the veterinarian will need its full medical history for signs of any underlying problems. A complete physical examination will be made of the cat. If the cat is suffering from traumatic injuries, life-threatening issues will be addressed first. In an attempt to identify any causative health issues, the vet will also complete a neurological evaluation and an otoscopic (ear) examination. Horner’s Syndrome will have to be differentiated from other problems that share symptoms such as ear infections, facial paralysis, and Key-Gaskell Syndrome. 

A phenylephrine test may be performed to locate any sympathetic nerve path damage. The longer the pupil takes to return to normal size after drop administration, the further from the eye that the damage is. Full blood work will be taken including a complete blood count and a biochemical profile to help identify any health issues in the body. Urinalysis may also be used for this purpose. If spinal cord or brain damage is suspected, cerebrospinal fluid samples may be collected for testing.

Horner’s Syndrome is a group of symptoms and not a disease itself. If no underlying cause can be identified, the issue may resolve on its own. Treatment of symptoms can provide relief as the cat experiences them. If a primary health issue has been found, proper treatment can reverse the syndrome. 

Eye Drops 

If the cat’s eyes are irritated from the many effects of Horner’s Syndrome, eye drops may be prescribed to help ease blinking and to soothe and minimize any ocular ulcers. If the cat is suffering from an inappropriately dilated pupil, phenylephrine drops may be used to correct the issue.

Surgical Removal

If a tumor has been identified as causing the nerve damage, removing it may relieve symptoms. This may or may not be possible depending on the location of the tumor. Surgery should only be performed if the risk is less severe than the symptoms that exist, or if the tumors are cancerous. General anesthesia is used for the procedure.

If your cat has undergone surgery, be sure to follow all at-home instructions for care. Monitor the incision site daily to check for swelling or bleeding. If tumors have been found as the cause of Horner’s Syndrome in your cat, prognosis may be guarded. If the syndrome was a result of trauma and the cat survives all other injuries, the chance of recovery is quite good. 

In cases which the syndrome develops suddenly and no cause is identified, the nerve issues may resolve on their own. Sometimes this can take up to 16 weeks to occur. In some instances, Horner’s Syndrome may be permanent due to irreversible damage, however, this is rare.