Trigeminal and Facial Nerves

Question 1

what is the key to recognizing problems in cranial nerves 5 or 7?

Answer 1

asymmetry in the face/head

atrophy: CN V mandibular branch
-temporalis
-masseter
-enophthalmos- pterygoid

droopy face: CN VII facial
-lip commissure
-ear position
-palpebral fissure (open wider bc lower lid sags due to orbicularis oculi muscle paresis/paralysis)

Question 2

describe the trigeminal nerve

Answer 2

1. exits from the pons (from brainstem, caudal to midbrain = ipsilateral deficits)
2. just prior to exiting the cranial cavity, splits into 3 branches
   -ophthalmic
   -maxillary
   -mandibular
3. provides sensory and motor innervation

-sensory: (GSA) cutaneous innervation to the head, all 3 branches
-opthalmic: eye, medial canthus, nasal mucosa
-maxillary: lateral canthus, skin lateral side of face (rostrally); PALPEBRAL REFLEX
-mandibular: skin over mandible, tongue, lateral caudal side of face (MUSCLE ATROPHY)

-motor (GSE): mandibular branch innervates temporalis, masseter, pterygoid muscles, rostral belly of digastricus

Question 3

how do you figure out if a CNV lesion is in the nerve or in the pons?

Answer 3

nerve: deficits just involving CN V

pons:
1. mentation
2. postural reaction deficits: ipsilateral
3. other cranial nerves
-V, VII, VIII

Question 4

describe trigeminal nerve sheath neoplasms

Answer 4

1. nerve sheath neoplasms most commonly affect nerves of the thoracic limb, but can also affect the pelvic limb or cranial nerve V!
2. signalment:
   -older dogs (>8-9 years)
   -no breed or sex
3. history:
   -chronic, progressive unilateral limb lameness (painful, thoracic > pelvic)
   -slow growing neoplasms! (metastasis not a concern)
4. treatment:
   -surgery: amputation or laminectomy and radiation
   -prognosis is worse the more proximal the lesion is
5. with cranial nerve V, can’t cut it out!
   -only treatment is radiation therapy or palliative therapy (corticosteroids if edema, eye lubricant bc dog doesn’t know to blink)
   -definitive care does help them survive for a longer time but clinical signs may not resolve
6. for very subtle changes on MRI, could just be neuritis but is hard to differentiate and can monitor and re-eval

Question 5

describe trigeminal neuritis

Answer 5

1. dogs (uncommon in other species)
2. ACUTE onset; difficulty eating (prehending food)
   -primarily mandibular branch
   -approx 1/3 cases have sensory deficits (can be asymmetrical)
   -very small percentage have Horner’s syndrome (sympathetic axons run with CN V ganglion)
3. diagnostic workup:
   -good physical exam: careful attention to lymph nodes
   -bloodwork: CBC, chem
   -MRI and/or CSF analysis
4. primary differential diagnosis: lymphoma
   -palpate LNs carefully, consider aspirating
   -careful attention to CBC and chem (hypercalcemia)
5. treatment:
   -supportive care: feeding/drinking, use liquid foods, hold head elevated and mouth closed, syringe feed water
   -spontaneous recovery in 2-3 weeks

Question 6

describe masticatory myositis

Answer 6

1. immune-mediated inflammation of the muscle of mastication
2. bilateral (rarely unilateral)
3. trismus: difficulty to open mouth; painful
   -differential diagnoses:
   –mechanical instability: TMJ disease
   –lock jaw: sublux/lux, OA, malformation
   –neoplasia (obstructing movement of mandible)
   –tetanus: rare and comes with other signs
4. signalment: large breed dogs > small breeds
   -german shepherds!
5. two clinical presentations:
   -acute: bilateral swelling of temporalis muscle (all muscles of mastication)
   -chronic: bilateral atrophy of the muscles of mastication
6. diagnosis: type 2M antibodies!!
7. treatment:
   -immunosuppressive corticosteroids
   -soft foods
   -chew toys = physical therapy
8. prognosis: good fore return of function

Question 7

what does EVERY animal with facial paralysis need? (2)

Answer 7

1. artificial tears
2. schirmer tear test

Question 8

describe unilateral facial nerve paresis/paralysis

Answer 8

differentials:
1. idiopathic
2. OMI
3. hypothyroidism

diagnostic steps/treatment:
1. idiopathic: ONLY facial nerve, no other cranial nerve dysfunction, exclude other causes
-MRI
-treatment: time! return of function variable, paralysis = usually not, paresis = some recover

2. OMI:
   -hx: allergic skin disease, ear infections
   -other cranial nerves: vestibular, Horner’s
   -OTOSCOPIC EXAM
   -MRI
   -treatment: surgery (bulla osteotomy, easy canal ablation)

EVERY PATIENT: otoscopic exam, ALWAYS provide eye lubricant, offer MRI always

Question 9

describe common signalment of facial nerve paresis/paralysis

Answer 9

breeds-dogs:
-beagle, boxer, cavie, cocker, pitbull

age: middle to older (5-10 years)

Question 10

describe hypothyroidism and the facial nerve

Answer 10

1. uncommon cause of facial nerve paralysis/paresis but is a common endocrine disorder of dogs
   -asymmetric facial nerve signs even though is endocrine!
2. may not have overt clinical signs or appearance of hypothyroidism
3. worth testing?
   -bloodwork: CBC = mild anemia, chemistry = increased triglycerides and cholesterol (fasting)
   -total T4, free T4, TSH level
4. treatment: supplementation, usually result sin return of function