PROVET HEALTHCARE INFORMATION - Horner's Syndrome

Horner's Syndrome

Note for Pet Owners:

This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Topics on this Page:

Description
Cause
Breed Occurrence
Signs
Complications

Diagnosis
Treatment
Prognosis
Long-term problems

Description
Horner's Syndrome is impairment of the sympathetic nerve supply to the eye and surrounding structures

Cause
The cause of Horner's Syndrome is impairment of the sympathetic nerve supply to the eye. This can occur anywhere along the neurological pathway :

Part 1. The Upper Motor Neurone section of the neural pathway involved starts in the hypothalamus of the brain and passes through the midbrain, brainstem and cervical spinal cord , ending in the preganglionic cell bodies in the thoracic spinal cord.

Upper Motor Neurone lesions following trauma, infarcts, neoplasia or inflammatory disease are rarely a cause of Horner's syndrome

Part 2 The Lower Motor Neurone section begins with the preganglionic cells in the grey matter of the spinal cord in the region of T1-T4. The axons leave the spinal cord and join spinal nerves at T1-T4 , pass through the chest and ventrolateral to the vertebral column as the sympathetic trunk , then along the neck as the vagosympathetic trunk. The sympathetic nerves which innervate the structures of the eye pass through the tympanoccipital fissure, into the middle ear and then on to form the ophthalmic nerve.

Intereference with the lower motor neurone section are the most common causes of Horner's Syndrome and may include :

Spinal cord injury at level T1-T4 - may be associated with limb paresis
Brachial plexus avulsion - may be associated with limb paralysis (same side)
Nerve sheath tumours at T1
Cranial mediastinal tumours eg thymoma, lymphoma
Injuries to the neck eg bite wounds, car accidents, post-surgery eg thyroidectomy
Neoplasia in the neck region
Otitis media - may be associated with vestibular syndrome and facial paralysis
Aural neoplasia - may be associated with vestibular syndrome and facial paralysis
Injury to the eye region, local neoplasia or abscess

Breed Occurrence
No breed predisposition has been reported

Signs
In dogs and cats Horner's Syndrome is characterised by the following changes involving the eye :

A constricted (miotic) pupil

Drooping of the upper eyelid (ptosis)

Sinking of the eyeball into the head (enophthalmus)

Protrusion of the third eyelid (nictitating membrane)

Complications
Depending upon the type and location of the primary lesion Horner's Syndrome may be complicated by the presence of :

Spinal cord injury at level T1-T4 - may be associated with limb paresis
Brachial plexus avulsion - may be associated with limb paralysis (same side)
Nerve sheath tumours at T1
Cranial mediastinal tumours eg thymoma, lymphoma
Injuries to the neck eg bite wounds, car accidents, post-surgery eg thyroidectomy
Neoplasia in the neck region
Otitis media - may be associated with vestibular syndrome and facial paralysis
Aural neoplasia - may be associated with vestibular syndrome and facial paralysis
Injury to the eye region, local neoplasia or abscess

Diagnosis
Dianosis is based upon the presenting signs and a complete physical examination and ophthalmologic, neurologic and otoscopic examination. Xrays of the chest may be required and other imaging tests such as CT or MRI scans may be necessary to identify lesions in the central nervous system.

Despite the use of these techniques in about 50% of cases in cats and dogs the primary cause can not be identified.

A very dilute sympathomimetic (eg 0.1% phenylephrine) can be applied to both eyes. The affected pupil will dilate within 20 minutes if the lesion is postganglionic (middle ear or retrobulbar). The normal pupil should not dilate. If neither dilate a stronger solution (10% phenylephrine) is applied to both eyes to confirm that they can dilate. However, this test is not reliable in all cases.

Treatment
In some animals the signs will resolve spontaneously without specific treatment.

If an underlying cause is found this should be treated appropriately.

Prognosis
The prognosis is good to guarded depending on the underlying cause fo the Syndrome

Long term problems
If the Syndrome does not resolve problems with tear overflow (epiphora) and secondary conjunctivitis may occur.

Updated October 2013