Cranial Neuropathy

Question 1

What’s the function and clinical manifestation of CN I?

Answer 1

Olfactory n,
sense of smell
disorder = inability to smell

Question 2

What’s the function and clinical manifestation of CN II?

Answer 2

Optic n,
vision
disorder = blind, dilated/ unresponsive pupils

Question 3

What’s the function and clinical manifestation of CN III?

Answer 3

Occulomotor n,
Eye movement (extra-ocular muscle) & pupil constriction (parasympathetic)
disorder: ventrolateral strabismus, dilated pupils, diminished/absent PLR

Question 4

What’s the function and clinical manifestation of CN IV?

Answer 4

Trochlear n,
Eye movement
disorder: dorsomedial strabismus

Question 5

What’s the function and clinical manifestation of CN V?

Answer 5

Trigeminal n.
Sensory to face;
motor to muscles or mastication
disorder: rubbing/pawing @ face, head muscle atrophy, dropped jaw if bilateral motor

Question 6

What’s the function and clinical manifestation of CN VI?

Answer 6

Abducent n.
Eye movement (lateral rectus & retractor bulbi)
disorder: medial strabismus

Question 7

What’s the function and clinical manifestation of CN VII?

Answer 7

Facial n,
Motor to facial expression, saliva and tear production (parasympathetic);
Sensory to rostral tongue
Disorder: inability to close eyelid, move ear, or retract lips; hemifacial tetany, deviation of the nasal philtrum (contralateral), dry eye, drooling

Question 8

What’s the function and clinical manifestation of CN VIII?

Answer 8

Vestibulocochlear n,
Balance and hearing
Disorder: head tilt, deaf, vestibular ataxia, positional strabismus, nystagmus

Question 9

What’s the function and clinical manifestation of CN IX?

Answer 9

Glossopharyngeal n.
Sensory and motor to the pharynx
Disorder: diminished gag reflex, difficulty swallowing

Question 10

What’s the function and clinical manifestation of CN X?

Answer 10

Vagus n
sensory and motor to pharynx, larynx, and viscera (movement of throat)
Disorder: loss of voice, coughing, regurgitation. Diminished gag reflex, dysphagia, laryngeal paralysis, megaesophagus

Question 11

What’s the function and clinical manifestation of CN XI?

Answer 11

Accessory n
motor to trapezius (movement of neck and shoulder)
Disorder: difficult to appreciate

Question 12

What’s the function and clinical manifestation of CN XII?

Answer 12

Hypoglossal n
Motor to tongue muscles
Disorder: atrophy of tongue, inability to retract tongue if bilateral; difficulty eating

Question 13

What changes can be noted on ophthalmic exam with optic neuritis?

Answer 13

Posterior segment of the eye:
- optic disc swelling
- vascular congestion
- hemorrhage
- peripapillary neuroretinitis

Question 14

What are some differentials for optic disc swelling?

Answer 14

papilledema/ optic nerve edema; accompanied by uveitis and glaucoma

Question 15

What are some causes of optic neuritis?

Answer 15

• Infectious (canine distemper, fungal, mycotic)
• immune-mediated
• tumour
• idiopathic

Question 16

How can you differentiate between optic neuritis and SARDS (sudden acquired retinal degeneration syndrome)?

Answer 16

Optic neuritis –> ERG = normal, SARDS ERG = extinguished

Question 17

What’s the prognosis for vision recovery with optic neuritis?

Answer 17

guarded to poor

Question 18

Which nerves innervate the extra-ocular muscles?

Answer 18

Oculomotor (CN III): pupil constriction
Trochlear (CN IV): eye position
Abducent (CN VI): eye position

Question 19

Which cranial nerves are involved in cavernous sinus (CSS) / orbital fissure (OFS) syndrome?

Answer 19

CN III, IV, VI, V (ophthalmic or maxillary branches)
Due to close proximity of these axons on the floor of the skull adjacent to the cavernous sinus prior to exiting the skull through the orbital fissure

Question 20

What are the clinical signs of cavernous sinus (CSS) / orbital fissure (OFS) syndrome?

Answer 20

• external and internal ophthalmoplegia (muscle paralysis)
• ptopsis
• reduced corneal sensitivity (CN V)
• neurotrophic keratitis

Question 21

What’s the most common cause of cavernous sinus (CSS) / orbital fissure (OFS) syndrome?

Answer 21

primary or metastatic tumour
in cats, infectious is possible too

Question 22

What’s the most commonly affected branch in trigeminal neuropathy?

Answer 22

Motor (mandibular branch); isolated sensory branches (ophthalmic / maxillary ) = rare

Question 23

What are some signs dysfunction of the mandibular branch of CN V?

Answer 23

• dropped jaw (flaccid bilateral paresis)

Question 24

What are some differentials for dropped jaw?

Answer 24

• mechanical jaw function (TMJ fracture/ avulsion)
• pain associated with jaw movement (myositis, retrobulbar mass)
• inflammatory (neospora, toxoplasma)
• idiopathic
• neoplastic

Question 25

What’s Pontomedullary syndrome?

Answer 25

If it’s not just peripheral CN V –> ie. involving pons
may have c/s due to dysfunction in CN VI-XII; central vestibular signs, and altered mentation (depressed)

Question 26

What’s the most common cause of trigeminal neuritis in the dog?

Answer 26

idiopathic
concurrent facial n. paralysis possible; Horner’s also possible

Question 27

What’s a common cause of acute, unilateral atrophy of the muscles of mastication?

Answer 27

Trigeminal nerve sheath tumour (ipsilateral)
- can have altered facial sensation (rubbing/ pawing at face; pain)
- Horner’s
- facial n involvement

Question 28

What are some signs of facial nerve paralysis/ neuropathy?

Answer 28

• acute inability to close the eyelids, drooping of ear/lip/ drooling (ipsilateral)

Question 29

What are some causes of facial neuropathy?

Answer 29

• otitis media/ interna
• trauma (bulla osteotomy)
• idiopathic (75% of dogs, 25% of cats)
• CN VIII can also be affected: vestibular signs

Question 30

What’s the prognosis of idiopathic facial neuropathy?

Answer 30

spontaneous recovery in dogs is possible: 3-8 weeks

Question 31

Which cranial nerves are involvement in swallowing?

Answer 31

CN IX, X, XI, XII

Question 32

What cranial nerves are involved in prehension of food?

Answer 32

Jaw (CN V), lip (CV VII), tongue (XII)

Question 33

What are some common causes of swallowing disorders?

Answer 33

• primary myopathies
• polyneuropathy
• neuromuscular junctional disorders
  caudal brain stem lesions

Question 34

Which CN innervate the esophagus?

Answer 34

XI and XII

Question 35

Which CN innervates the larynx?

Answer 35

XII, and recurrent laryngeal nerve

Question 36

What are the clinical signs associated with Horner’s Syndrome?

Answer 36

• ptosis
• enophthalmos
• prolapsed 3rd eyelid
• miosis (small pupil)

Question 37

Describe the 3-neuron oculosympathetic pathway.

Answer 37

1st order neuron: UMN/ central, originates in the rostral brainstem –> goes down spine to synapse on 2nd order: cell bodies located in T1-T3 –> goes up via the vagosympathetic trunk to synapse on the 3rd order: post-ganglionic neurons in the cranial cervical ganglion –> projects to eye and adnexa

Question 38

How can pre- vs post-ganglionic disorders be differentiated?

Answer 38

Phenylephrine test
If mydriasis develops within 20min, then it’s post ganglionic. If it takes more than 20min, then it’s pre-ganglionic