Equine - Peripheral Nerve Dz

Question 1

List the clinical signs of Horner’s Syndrome in the horse.

Answer 1

Unilateral sweating, regional hyperthermia, ptosis, miosis, enophthalmus, protrusion of the third eyelid, congested mucous membranes, inspiratory stridor, dermatitis caused by chronic sweating.

Question 2

List primary conditions which can result in Horner’s Syndrome in the horse.

Answer 2

• Guttural pouch disease.
• Perivascular injection (jugular v).
• Thoracic inlet masses.
• Trauma to the basisphenoid area or cervical trauma.
• Otitis media.
• Periorbital masses or abscesses.
• Parotid duct obstruction and inflammation.
• Oesophageal rupture.
• Complications associated with carotid a ligation.
• Polyneuritis equi (rarely).

Question 3

Horner’s Syndrome results from interruption of ocular sympathetic pathways. Describe the anatomy of this pathway.

Answer 3

• 1st order: tectum of midbrain –> axons descend to T1-T3 –> enter grey matter of dorsal horn, synapse on…
• 2nd order: pre-ganglionic sympathetic motor neurons –> cervicothoracic and middle cervical ganglia –> ascend in cervical sympathetic trunk to cranial cervical ganglion (guttural pouch)–> synapse on…
• 3rd order: post-ganglionic sympathetic nerve –> fibres distributed to sweat glands of head, ciliary muscles, periorbital smooth muscles.

Question 4

Correlate the site of damage with classification of Horner’s Syndrome by ‘order’.

Answer 4

• 1st order: brainstem or spinal cord.
• 2nd order: cranial thoracic nerve roots or spinal nerves or cervical sympathetic trunk.
• 3rd order: cranial cervical ganglion, the skull, behind the eye.

Question 5

Describe how you can use ocular pharmaceutics to determine the level of sympathetic interruption in a horse with Horner’s Syndrome.

Answer 5

• Hydroxyamphetamine 1%: results in release of NE from intact post-ganglionic neurons –> mydriasis.
• 0.1ml 1:1000 epinephrine: mydriasis in 20mins post-ganglionic lesion vs 40 mins pre-ganglionic lesion.

Question 6

Describe treatment and prognosis of Horner’s Syndrome in horses.

Answer 6

• Usually irreversible, unless associated with perivascular xylazine inj.
• If perivascular inj: infiltrate large volumes of saline into perivascular tissues.
• Anti-inflammatory doses of flunixin and dexamethasone.
• Drain abscesses.
• Treat GP mycosis.