Cranial nerves and their disorders

When to refer Bell's palsy urgently to ENT or neurology

Diagnostic uncertainty. Bilateral. Recurrent. Paralysis not improving after 1 month.

Causes of vestibulocochlear (8th) nerve palsy

Loud noise. Paget's disease of the bone. Meniere's disease. Herpes zoster. Neurofibroma. Acoustic neuroma. Brainstem CVA. Lead. Aminoglycosides, furosemide, aspirin.

Signs of vagus (10th) nerve palsy

Palatal weakness can cause "nasal speech" and nasal regurgitation of food. Unilateral lesion: palate moves asymmetrically towards the good side when the patient says 'ahh'. Bilateral lesion: uvula does not lift. Recurrent nerve palsy results in hoarseness, loss of volume and "bovine cough".

Causes of isolated spinal accessory (11th) nerve palsy

Same as vagus nerve.

Causes of bilateral facial nerve palsy

Sarcoidosis. Guillain-Barre syndrome. Polio. Lyme's disease. HIV.

Optic nerve - testing and signs of injury

See ophthalmology notes on eye examination and revision sheets.

Testing the 3rd, 4th and 6th cranial nerves

See ophthalmology notes on eye examinations.

Why is vertical gaze often impaired after orbital floor fracture?

Entrapment of inferior rectus.

Sequelae of Bell's palsy

16% have: - facial asymmetry - gustatory lacrimation - inadequate lid closure - brow ptosis - drooling - hemifacial spasm

Trigeminal (5th) nerve palsy signs

1st sign of ophthalmic branch lesion: loss of corneal reflex. Reduced sensation or dysasthesia (an abnormal unpleasant sensation felt when touched) over affected area. Weakness of jaw clenching and side-to-side movement. LMN lesion: jaw deviates to weak side when mouth opened. There may be fasciculation of temporalis and masseter.

Testing the spinal accessory (11th) nerve

2 ways of testing sternocleidomastoid: - ask patient to flex their neck whilst you resist the movement with you hand against their forehead - place a hand on the patient's right temple and ask them to turn their head to the right Testing trapezius: ask the patient to shrug their shoulders.

Oculomotor (III) nerve palsy signs

3rd nerve insults can lead to either a complete or partial nerve palsy depending on the severity of the insult. Horizontal and vertical diplopia. Can involve the pupil or spare it: - pupil-controlling parasympathetic fibres are found on the outside of the 3rd nerve - non-pupil affecting fibres are usually more central and are the first to be affected by blockage to the blood supply - therefore, early pupil dilation implies compressive lesion whereas DM and other vascular causes do not cause a dilated pupil - if the ocular sympathetic fibres are also affected behind the orbit, the pupil will be fixed but not dilated - pupil will always be fixed and not able to accommodate Complete ptosis. Complete internal ophthalmoplegia (masked by ptosis) - unopposed lateral rectus and superior oblique cause DOWN AND OUT deviation of eye

What is Gradenigo's syndrome?

5th + 6th nerve palsies, caused by lesions within the petrous temporal bone.

Anatomy of eye movements

6 external ocular muscles. - 4 rectus muscles pull directly on the globe so that they move the eye in the direction of their name: superior, inferior, medial, lateral (the superior and inferior recti are not placed centrally so they have a tendency to move the eyeball medially but this is opposed by the 2 oblique muscles). - 2 oblique muscles move the eye outwards as well as up and down. -- each hooks round a "pulley" so that it moves the eye the opposite way to which its name suggests -- superior oblique abducts, depresses and internally rotates the eye -- inferior oblique abducts, elevates and externally rotates the eye

Supranucleur abnormalities

Abnormality of voluntary or pursuit eye movements but eye movements can be produced by the doll's head manoeuvre.

Features of LMN facial nerve palsy

Affects all facial muscles. Weakness of the muscles of facial expression (cannot wrinkle forehead) and eye closure. The face sags and is drawn across to the opposite side on smiling. Voluntary eye closure may not be possible and dry eyes - can produce damage to the conjunctiva and cornea (e.g. exposure keratitis). Bell's sign: upward gaze on attempted eye closure. Can cause an impaired corneal reflex as the ipsilateral orbicularis oculi cannot contract properly. In severe cases, there is often loss of taste over the anterior two thirds of the tongue, intolerance to high-pitched or loud noises (AKA hyperacusis) and crocodile tears (crying when hungry).

Testing the vagus (10th) nerve

Assess palatal movement by asking the patient to open their mouth wide and say "ahh" - the uvula will normally lift centrally. Assess laryngeal function by asking the patient to speak and cough.

Investigations after diagnosis of 4th or 6th cranial nerve palsy

BP, fasting glucose, cholesterol, ESR, ANAs, venereal disease tests, + imaging if doesn't resolve by 3 months or <50yo.

Vertical gaze palsy

Bilateral. Inability to look up or down. Inability to look down can lead to falling down stairs. Pupils often unequal but fixed. Usually no diplopia. Causes: Parkinson's, progressive supranuclear palsy.

Function of vestibulocochlear (8th) nerve

Carries 2 groups of fibres, those to the cochlea (hearing) and to the semicircular canals (balance and posture).

Internuclear ophthalmolplegia

Caused by MLF lesions. The lateral gaze nucleus in the pons stimulates the ipsilateral 6th nerve nucleus, causing the ipsilateral eye to abduct, but the message fails to reach the opposite 3rd nerve nucleus and so the contralateral eye does not adduct. Binocular horizontal diplopia. When asked to look to the side where the diplopia is worse, the eyes DIVERGE. Associated with ataxic nystagmus in the abducting eye.

Causes of unilateral lower motor neurone facial nerve palsy

Causes of bilateral facial nerve palsy. Bell's palsy (idiopathic). Cerebrovascular disease e.g. brainstem stroke. Ramsay-Hunt syndrome (due to herpes zoster). Herpes simplex/zoster, EBV, CMV. Acoustic neuroma. Parotid/posterior fossa/cerebellopontine tumours. MS. DM. Hypertension in pregnancy. Sjogrens, RA. Iatrogenic: LA for dental treatment, linezolid. Base of skull fractures. Otitis media or cholesteatoma.

What pathology causes a 7th and 8th, and then 5th and sometimes 9th nerve palsy?

Cerebellopontine angle tumours.

Voluntary and involuntary/emotional movements in facial nerve palsy

Cerebrovascular accidents usually weaken voluntary movement but spare involuntary/emotional movements e.g. spontaneous smiling. The much rarer selective loss of involuntary/emotional movement is called "mimic paralysis" and is usually due to a frontal or thalamic lesion.

Functions of oculomotor (III) nerve

Eye movement (SR, IR, MR, IO). Pupil constriction. Accommodation. Eyelid opening (supplies levator palpebrae superioris muscle).

Trigeminal (V) nerve function

FORMS 3 TRUNKS... Ophthalmic division: - sensory fibres to the skin over medial nose, forehead and eye (including corneal reflex) - sympathetic fibres for pupil dilation Maxillary division: - sensory fibres to the skin over the upper lip and palate, cheek and the triangle of skin extending from the angle of the eye to the apex in the mid-temporal region - parasympathetic supply to lacrimal gland Mandibular division: - sensory fibres to the skin over the lower lip and chin up to and including the tragus and upper part of the pinna, mucous membranes of the floor of mouth/cheek/anterior 2/3s of tongue - motor fibres to massester, temporalis and pterigoids

Function of the facial (7th) cranial nerve

Face: muscles of facial expression, including obicularis oculi. Ear: nerve to stapedius muscle. Taste: supplies anterior 2/3s of tongue. Tear: parasympathetic fibres to lacrimal glands and salivary glands.

What does diplopia with new onset headache and scalp tenderness suggest?

GCA.

Abducens (6th) nerve palsy signs

Horizontal diplopia (worse on gazing towards affected side and to the distance). Inability to look laterally so when asked to look towards the side with the problematic eye, the eyes converge. Eye deviated medially because of unopposed action of the medial rectus muscle. Occasionally head posture towards affected side.

System used for describing the degree of paralysis with facial nerve palsy

House-Brackmann scale. 1 = total power, 6 = total paralysis.

Downgaze paresis

Inability to look down. Due to lower brainstem lesions.

Upgaze paresis

Inability to look up. Due to upper brainstem lesions.

What does combined 3rd, 4th and 6th nerve palsies suggest?

Intracranial or meningeal tumour. Stroke. Aneurysms. Meningitis. Cavernous sinus lesion. Wernicke's encephalopathy. MS. Myasthenia gravis. Muscular dystrophy. Myotonic dystrophy. Guillain-Barré syndrome. Trauma and orbital pathology.

Prognosis of cranial nerve palsies associated with DM or hypertension

Isolated and associated with DM or hypertension: likely to recover within 6 months. 6th nerve palsy of vascular cause tends to resolve in 6-8 weeks. Imaging required if: - resolution doesn't occur within months - condition progresses - additional neurological signs or symptoms develop

Causes of isolated glossopharyngeal (9th) nerve palsy

Isolated nerve lesions VERY RARE. Trauma. Brainstem lesions. Cerebellopontine angle and neck tumours. Polio. Gullain-Barré syndrome.

Causes of isolated vagus (10th) nerve palsy

Isolated nerve lesions VERY RARE. Same causes as glossopharyngeal nerve.

Signs of spinal accessory (11th) nerve

LMN lesion: ipsialteral weakness and wasting of sternocleidomastoid and trapezius causing weakness of shrugging shoulders and head turning. UMN lesion: ipsilateral sternocleidomastoid and contralateral trapezius weakness and wasting.

Signs of hypoglossal (12th) nerve palsy

LMN lesion: wasting + fasciculation of ipsilateral side of tongue and on attempted protrusion of the tongue it deviates TOWARDS the affected side. UMN: on attempted protrusion of the tongue it deviates AWAY from the affected side + slow moving (no wasting or fasciculations).

Weber's and Rinne's tests

Look at ENT notes.

Testing the hypoglossal (12th) nerve

Look at the tongue for wasting and fasciculations when at rest in the mouth. Ask the patient to put out their tongue and move it quickly from side to side, watching the speed of tongue movement.

Facial nerve palsy investigations

Look for facial asymmetry. Compare blink rate of eyes. Ask patient to: - give a big grin showing their teeth - full and symmetrical smile? - blow out their cheeks - screw up their eyes (and then the examiner should try and prise them open gently) - raise their eyebrows - symmetrical forehead furrows? Ask patient if they have noticed any change in taste or being troubled by loud noises. Serology: Lyme's, herpes simplex and herpes zoster. Check BP in children with Bell's palsy.

Causes of recurrent facial nerve palsy

Lymphoma. Sarcoidosis. Lyme's disease.

Causes of isolated abducens (6th) nerve palsy

MS. Pontine stroke. Nasopharyngeal carcinoma. Skull # involving petrous temporal bone. Considered a false localising signs in raised ICP (due to its long extracerebral course).

Causes of unilateral upper motor neurone facial nerve palsy

MS. Stroke. Intracranial tumours. Syphilis. HIV. Vasculitis.

Lateral gaze palsies

Means that neither eye can look in one direction. Caused by lesions of the nucleus for lateral gaze.

Risk factors for cranial nerve palsies

Microvascular disease (present in 60% of cases): - DM - hypertension MS. Guillain-Barré syndrome. Temporary palsy of a single ocular nerve is not uncommon (may be of unknown cause). Lyme disease. Syphilis. Vasculitis e.g. polyarteritis nodosa, GCA. Meningitis - chronic meningitis (malignant, TB, or fungal) tends to pick off the lower cranial nerves one by one. Cranial space-occupying lesion. Raised ICP. Nerves trapped after traumatic orbital fracture.

Bell's palsy epidemiology

Most common cause of acute LMN facial nerve palsy. Often preceded by discomfort/pain around the mastoid. Probably due to ischaemic compression of the facial nerve within the facial canal, as a result of inflammation, most likely due to herpes simplex infection. Typically 30yo. Most common in pregnant women. Low rate of recurrence.

Function of the spinal accessory (11th) nerve

Motor fibres to sternocleidomastoid and trapezius.

Function of vagus (10th) nerve

Motor fibres to the palate and vocal cords. Sensory fibres to posterior and floor of external acoustic meatus. Also contains visceral afferent and efferent fibres. It leaves the skull through the jugular foramen, passes within the carotid sheath in the neck (giving off cardiac branches, and the recurrent laryngeal nerves supplying the vocal cords), through the thorax supplying the lungs, and continues on via the oesophageal opening to supply the abdominal organs.

Function of the hypoglossal (12th) nerve

Motor fibres to the tongue and most of the infrahyoid muscles.

Causes of olfactory nerve injury

Nasal and sinus disease (most common). Trauma e.g. to the cribiform plate severing the olfactory sensory axons. Frontal lobe tumour. Meningitis.

Nerve supply to extraocular muscles

Oculomotor (3rd cranial) nerve: - superior rectus - inferior rectus - medial rectus - inferior oblique Trochlear (4th cranial) nerve: - superior oblique Abducens (6th cranial) nerve: - lateral rectus

Olfactory (I) nerve anatomy

Olfactory cells are a series of bipolar neurones which pass through the cribiform plate to the olfactory bulb.

Trochlear (4th) nerve palsy causes

Orbital trauma most commonly. Congenital (rare). + general causes of cranial nerve palsies.

Common causes of facial nerve palsy in children

Otitis media. Lyme's disease.

Investigations following diagnosis of 3rd cranial nerve palsy

Painful or pupil-involving: urgent MRI or MRI angiogram to exclude posterior communicating artery aneurysm. Pupil-sparing: BP, fasting glucose, cholesterol, ESR, ANAs, venereal disease tests, + imaging if doesn't resolve by 3 months or <50yo.

A unique cause of oculomotor (3rd) nerve palsy compared to 4th and 6th nerve

Posterior communicating artery aneurysm.

Risk factors for Bell's palsy

Pregnancy. DM.

Causes of isolated hypoglossal (12th) nerve palsy

RARE. Polio. Syringomyelia tuberculosis. Median branch thrombosis of the vertebral artery.

Trochlear (4th) nerve palsy signs

Rare. Most common cause of pure VERTICAL diplopia (due to weakness of downward and inward eye movement). Diplopia worse in adduction and depression so activities such as reading and walking down stairs may exacerbate symptoms. Patient tends to compensate by tilting head away from affected side.

Bell's palsy management

Reassurance that most cases fully resolve spontaneously within 6 weeks. Eye care: lubricating drops and eye ointment at night. Steroids within 72 hours for about 10 days. Botulinum toxin or surgery (facial nerve decompression) may be required.

Signs of olfactory nerve injury

Reduced taste and smell, but not to ammonia which stimulate the pain fibres carried in the trigeminal nerve.

Function of glossopharyngeal (9th) nerve

Sensory fibres from the tonsils, posterior pharynx, middle ear and posterior 1/3 of the tongue. Visceral sensory fibres from posterior 1/3 of tongue (i.e. taste), carotid bodies and carotid sinus. Parasympathetic fibres to parotid gland. Motor fibres to stylopharyngeus muscle.

Causes of trigeminal (5th) nerve palsy

Sensory: trigeminal neuralgia, herpes zoster, nasopharyngeal carcinoma. Motor: bulbar palsy, acoustic neuroma.

Features of UMN facial nerve palsy

Spares upper face muscles i.e. forehead - can wrinkle forehead and raise eyebrows and sagging of face not as prominent.

Function of abducens (6th) nerve

Supplies lateral rectus muscle of the orbit.

Function of trochlear (4th) nerve

Supplies superior oblique muscle of the orbit.

Testing the trigeminal nerve

Test sensation to pinprick, light touch and temperature in each division: - ophthalmic: above eyebrows - maxillary: over zygoma - mandibular: chin either side of midline Corneal reflex can be tested by touching the cornea with cotton wool - the normal response is a brisk contraction of both orbicularis oculi. it can also be tested indirectly by touching the inside of the nostrils with a wisp of cotton wool. Jaw jerk tested by asking the patient to let their jaw hang open, placing your thumb on the patient's chin and then briskly striking your thumb with a tendon hammer. Mandibular branch motor function can be tested by getting the patient to clench their teeth and feeling the massester and temporalis, and pushing upwards on the bottom of the patient's chin and asking them to open their jaw.

Testing the glossopharyngeal (9th) nerve

Tested as part of the gag reflex - touching the posterior pharynx with a tongue depressor (sensed by the glossopharyngeal nerve) normally provokes pharyngeal movement (caused by the vagus nerve) - however, 20% of normal people have a minimal/absent response. Test speech and swallowing ability.

Signs of glossopharyngeal (9th) nerve palsy

Unilateral lesion: no deficit because of bilateral corticobulbar connections. Bilateral lesion: pseudobulbar palsy, loss of taste on posterior 1/3 of tongue, loss of gag reflex, dysphagia, carotid sinus dysfunction.

Signs of vestibulocochlear (8th) nerve palsy

Unilateral sensorineural hearing loss. Tinnitus.

Testing the olfactory nerve

Usually only tested formally in patients with specific complaints regarding their sense of smell. Before starting, check that there is free flow of air by occluding each nostril in turn and asking the patient to sniff in. Presented with a range of smells to each nostril while closing off the other and asking the patient to identify them. Ammonia is also tested: this is not perceived by the olfactory nerve but is a direct irritant to the nasal mucosa, stimulating the trigeminal nerve. Failure to respond to ammonia suggests non-organic anosmia or malingering.

Features of diplopia due to myasthenia gravis

Varying diplopia depending on the muscles affected. Better after rest and worse at end of day or during retesting due to fatigue. May also have more systemic features including bilateral ptosis and dysphagia. May be unable to "bury the eyelashes" (orbicularis muscle - VII nerve innervation).

Types of eye movements

Voluntary AKA saccadic (e.g. told to look right) - initiated from frontal eye fields. On pursuit AKA following objects - controlled by occipital lobe. Reflex movements to maintain eye posture with the head and other movements - under vestibular control and tested as the vestibulo-ocular reflex (doll's head manoeuvre). These movements are integrated in the brainstem with the 3rd and 4th nuclei in the midbrain and the parapontine reticular formation and the 6th nerve nucleus in the pons. These are connected by the median longitudinal fasciculus (MLF).