Introduction

• Common unilateral neurological disorder of eye - can sometimes be bilateral.
• Cause: most common cause is idiopathic Horner syndrome - potentially lesion anywhere along the sympathetic pathway to the eye (brainstem, cervical spinal cord, T1-T3 spinal cord, brachial plexus, intrathoracic, vagosympathetic trunk, middle ear, retrobular).
• Signs: ptosis upper eyelid, miosis, enophthalmos, protrusion of third eyelid (due to enophthalmos and nictitans muscle relaxation in cats), conjunctival hyperemia in some animals.
• Diagnosis: sometimes can identify location of injury pharmacologically, more usually by other associated clinical signs.
• Treatment: specific treatment for underlying disease if it can be ascertained; clinical signs can often be improved with topical phenylephrine.
• Prognosis: can recover over protracted period, depending on site and nature of lesion.

Pathogenesis

Etiology

• Idiopathic most common cause in dogs.
• Brainstem trauma Brainstem: contusion , neoplasm, infection or inflammation.
• Neurological infection, eg Neospora infection Neosporosis.
• Cervical spinal cord trauma Spinal cord: concussion, disk herniation, acute non-compressive nuclear disk extrusion, neoplasm, fibrocartilagenous embolism (FCE) Fibrocartilaginous embolism.
• T1-T3 trauma, disc, neoplasm, FCE.
• Brachial plexus avulsion Brachial plexus: avulsion.
• Brachial plexus tumor Shoulder: brachial plexus tumor.
• Vagosympathetic trunk trauma or cranial mediastinal neoplasm Mediastinal disease.
• Cranial cervical ganglion injury.
• Middle ear trauma, neoplasm, otitis media Otitis media /interna Otitis interna
• Retrobulbar trauma, neoplasm Retrobulbar: neoplasia , abscess Retrobulbar space-occupying lesions.
• Compromise (usually compression) of any of the descending neurons, axons in the pathway.
• Thoracic neoplasia.
• Mediastinal mass Mediastinal disease.
• Spinal neoplasia.
• Disk disease Intervertebral disk: type 2 herniation.
• Otitis media Otitis media.
• Iatrogenic following venipuncture using jugular vein.

Predisposing factors

• Dogs with a tendency to develop spinal cord and middle ear disease are at risk.

Pathophysiology

• Pathological change at one of several sites → failure of sympathetic nerve supply to eye and surrounding structures → loss of smooth muscle tone → clinical signs.
  • First order: hypothalmus to T1-T3 spinal cord lesions.
  • Second order: thoracic sympathetic trunk to cranial cervical ganglion lesions.
  • Third order: post-ganglionic fibers arising at cranial cervical ganglion rostrally up to the eye.

Timecourse

• Slow recovery over many months depending on etiology and treatment.

Diagnosis

Treatment

Outcomes