Cranial Nerves

Question 1

Causes of Optic Neuropathy

Answer 1

If <50, most likely demyelinating cause (e.g. MS, NMO)

If > 50, most likely ischaemic cause e.g. GCA

Inflammatory Causes
- Sarcoidosis, vasculitides

Infective Causes
- Syphilis, TB, lyme disease

Compressive Causes
- Tumours (e.g. Optic glioma), dysthyroid eye disease, pituitary tumour

B12 Deficiency

Toxic Causes
- Methanol, Ethambutol

Question 2

Optic Neuropathy - Features

Answer 2

Subacute loss of vision
- Usually painless
Reduced visual acuity, especially central
Afferent pupillary defect
Pale optic disc +/- cupping

Question 3

Function of CNIII

Answer 3

CN III = oculumotor nerve

Controls 4 of the 6 extraocular muscles
(MR, IO, SR and IR)

Pupil constriction and accommodation (parasymp)

Eyelid opening (levator palpebrae)

Question 4

Features of a Compressive (“Complete”) CN III Palsy

Answer 4

Complete ptosis
Pupil on affected side dilated and non reactive to light
Eye on affecting side “down & out”

{Why?
- Parasympathetic fibres responsible for pupillary response are on outside of nerve and most superficial = affected by compression!}

Question 5

Features of a “Medical” CN III Palsy
(Partial)

Answer 5

Complete/partial ptosis
Pupil on affected side is normal and reacts to light
Eye “down and out”

Parasympathetic nerve fibres on CNIII have different blood supply

Question 6

Medical causes of a CN III palsy

Answer 6

Diabetes Mellitus
MS
Vasculitides
Amyloidosis
Ischaemic stroke
- If also has contralateral hemiparesis = Weber’s (midbrain stroke)

Question 7

Investigating CN III palsy

Answer 7

Key Qs - is it compressive? are there other palsies present?

COMPRESSIVE LESION
- Urgent MRI/MRA/CT angiogram
- Neurosurgical input
Rx depends on lesion found

SOLITARY PUPIL SPARING CN III PALSY
- Cardiovascular work up = ECG, BP, glucose, Hb1AC, lipids
- Optimise CVD RFs
- If not resolved in 3 months or no obvious CVD RFs = vasculitis screen and MRI (?MS)

Question 8

Differentials for Ptosis

Answer 8

UNILATERAL PTOSIS
CN III palsy
Horner’s syndrome (constricted pupil)

BILATERAL PTOSIS
Myasthenia gravis (usually bilateral, fatiguability)
Myotonic dystrophy (usually bilateral)
Congenital
Miller- Fischer

Question 9

Function of CN IV

Answer 9

= Trochlear nerve

Controls Superior Oblique extraocular muscle (SO4) = depression, intorsion and adduction of the eye

Longest intracranial nerve

Question 10

Features of CN IV Palsy

Answer 10

Affected eye is “upwards and outwards”
Head tilt away from affected side
Defective downward gaze = vertical diplopia (exacerbated by walking downstairs/reading)
Failure of intorsion
- “Follow my finger” as you draw an upwards arc from pts ear to nose

Question 11

Function of CN VI

Answer 11

= Abducens palsy

Controls Lateral Rectus muscle (LR6) = ABduction

Adbucens nucleus = in pons

Question 12

Features of CN VI palsy

Answer 12

Affected eye rests in adduction
Inability to abduct affected eye
Horizontal diplopia

Question 13

Internuclear Ophthalmoplegia

Answer 13

Due to damage to medial longitudinal fasciculus (MLF)
= connection between nuclei of CN III and VI

Can be demyelinating, ischaemic, neoplastic or inflammatory lesion in pons/midbrain

FEATURES
- Inability to adduct affected eye (ipsilateral)
- Nystagmus in contralateral eye when trying to look to affected side

Question 14

Function of CN V

Answer 14

= Trigeminal nerve

Facial sensation
Muscles of mastication
Corneal reflex

Question 15

Function of CN VII

Answer 15

= Facial Nerve

“Face, ears, taste, tears”
- Muscles of facial expression
- Stapedius (loud noises)
- Anterior 2/3 of tongue
- Lacrimal and salivary glands

Question 16

Features of CN VII Palsy

Answer 16

Facial muscle weakness
- Forehead sparing if UMN
Bell’s phenomenon
= eye rolls upwards when trying to close eye (LMN)
Reduced sense of taste
Sensitive to loud noises (hyperacusis!)

Question 17

Causes of LMN CN VII Palsy

Answer 17

Idiopathic (Bell’s palsy)
Ramsay Hunt Syndrome (Herpes zoster)
Diabetes
Infection - HIV, lyme disease, TB
Sarcoidosis
Vasculitides
Space Occupying lesion
- Acoustic neuroma
- CPA tumour
- Parotid tumour
GBS

Question 18

Causes of UMN CN VII Palsy

Answer 18

Lesion of CN VII nucleus e.g. stroke, MS, space occupying lesion

Question 19

Is a UMN facial nerve palsy or LMN facial nerve palsy “forehead sparing”?

Answer 19

UMN is forehead sparing
- CN VII nucleus for upper face receives input from both cerebral hemispheres

Question 20

Bell’s Palsy

Answer 20

Idiopathic facial nerve palsy
LMN

Increased risk if
- HTN, diabetes, pregnant, FHx, black/hispanic ethnicity

FEATURES
- Rapid onset <72 hours
- Facial muscle weakness (NO forehead sparing)
- Facial/ear/postauricular pain
Difficulty chewing
Change in taste sensation
Incomplete eye closure
Bell’s phenomenon
Hyperacusis

MANAGEMENT
Prednisolone e.g. 60mg for 5 days
Eye care e.g. tape, drops

If untreated 15% have permanent facial weakness

Question 21

Red flag features in Bell’s Palsy

Answer 21

UMN features e.g. ataxia, limb weakness
Painful facial paralysis
Suspicious head and neck lesion
Unilateral hearing loss (?involvement of CN VIII)
Bilateral
No improvement after 3 weeks
Recurrent
Systemically unwell

Question 22

Function of CN VIII

Answer 22

= Vestibulocochlear nerve

Hearing and balance

Question 23

Function of CN IX

Answer 23

= Glossopharyngeal nerve

Posterior 1/3 of tongue taste
Pharyngeal muscles
(Muscles of swallowing and speech)

Question 24

Function of CN X

Answer 24

= Vagus nerve

Provides motor innervation to the majority of the muscles of the pharynx, soft palate and larynx
(Muscles of swallowing)
Innervates the smooth muscle of the trachea, bronchi and gastro-intestinal tract and regulates heart rhythm

Question 25

Function of CN XI

Answer 25

= Accessory Nerve

Sternocleidomastoid and trapezius muscle movement
= turning head and shrugging shoulders

Question 26

Function of CN XII

Answer 26

= Hypoglossal nerve

Motor innervation of the vast majority of the muscles of the tongue
- Tongue deviates towards side of lesion