Cranial nerve palsies

Cranial nerve palsy is characterized by a decreased or complete loss of function of one or more cranial nerves. The etiology may be congenital or acquired. Multiple cranial neuropathies are common, particularly in lesions arising from tumors, trauma, impaired blood flow, and infections. While a diagnosis can usually be made based on clinical features, further investigation is often warranted to determine the specific etiology, which should determine the course of treatment.

A useful mnemonic to remember the function of all the 12 cranial nerves is “Some Say Marry Money, But My Brother Says Big Brain Matters More”: CN I is sensory, CN II is sensory, CN III is motor, CN IV is motor, CN V is both (mixed), CN VI is motor, CN VII is both (mixed), CN VIII is sensory, CN IX is both (mixed), CN X is both (mixed), CN XI is motor, and CN XII is motor.

Remember that CN VII (Seven) controls Salivation by innervating Submandibular and Sublingual glands.

References:^[1][2][3]

A cranial nerve mononeuropathy is a condition in which only a single cranial nerve or nerve group is damaged. The clinical presentation of cranial nerve mononeuropathies depends on the underlying cause as well as the region that is affected along its pathway.

• Etiology
  • Trauma: especially impact to the lateral and occipital regions (e.g., ethmoid bone fracture)
  • Neurodegenerative diseases (e.g., Alzheimer disease)
  • Congenital (e.g., Kallmann syndrome)
  • Intracranial space-occupying lesion
• Clinical features: anosmia

• Etiology
  • Ischemic optic neuropathy (i.e., caused by microvascular disease)
  • Inflammation: multiple sclerosis, sarcoidosis, viral infections (e.g., measles, mumps)
  • Trauma
  • Tumors (e.g., optic nerve glioma)
  • Impaired nutrition: vitamin B deficiency
  • Drugs: sildenafil; , amiodarone; , ethambutol
• Clinical features: impaired vision
  • Complete transection → ipsilateral blindness + loss of direct pupillary light reflex
  • Increased intracranial pressure → papilledema
  • Compression (e.g., tumor) → optic atrophy

Neuroanatomy

Isolated oculomotor nerve palsy

• Etiology
  • Ischemic microangiopathy (more common in patients above the age of 60)
    • Diabetic cranial mononeuropathy
    • Hypertension
  • Compression or transection
    • Posterior communicating artery aneurysm
    • Base of skull fractures
• Clinical features
  • Paralytic squint
    • Adduction weakness
    • The affected eye looks outwards (exotropia) and downwards (hypotropia)
  • Ptosis
  • Horizontal diplopia that is worse when the head is turned away from the side of the nerve palsy
  • Pupillary involvement
    • Compressive lesions: a non-reactive, dilated pupil
    • Ischemic microangiopathy: typically sparing of the pupil
• Diagnostics
  • A dilated pupil → often a compressive lesion (e.g., posterior communicating artery aneurysm)
    • Best initial test: urgent MRI with MR angiography
    • If MRI is normal: perform a lumbar puncture
  • Pupillary sparing → often due to ischemic microangiopathy
    • Assess risk factors for atherosclerosis or arteritis (e.g., blood pressure, glucose, ESR, lipid profile)
    • If no recovery at 3 months: perform an MRI
• Treatment
  • Compressive lesions: surgery
    • Posterior communicating artery aneurysm: urgent neurosurgical clipping or endovascular coiling
  • Ischemic microangiopathy or demyelinating lesions: medical management with adequate control of the underlying disease

For more details about oculomotor nerve lesions and drugs affecting pupillary size, see the article pupillary abnormalities.

With an isolated ocuLOVEmotor nerve palsy, nobody loves you when you are down and out (the pupil points outwards and downwards)!

Compression of the oculomotor nerve can cause isolated pupillary dilation due to injury of the parasympathetic fibers. Microangiopathy (e.g., due to diabetes mellitus) typically affects the deeper somatic fibers first, causing ophthalmoplegia without pupillary dilation.

• Etiology
  • Acquired
    • Microvascular damage (diabetes, hypertension, arteriosclerosis)
    • Cavernous sinus thrombosis
    • Trauma
  • Congenital: fourth nerve palsy
• Clinical features
  • Extorsion of the eye: inability to depress and adduct the eyeball simultaneously
  • Diplopia
    • Vertical or oblique diplopia
      • Exacerbated on downgaze (e.g., reading) away from side of affected muscle ^[4]
      • Worsens when patient turns the head towards the paralyzed muscle → head tilt to the opposite side of the lesion
  • Mild esotropia ^[5]

• Etiology
  • Tumor
  • Vascular compression of the nerve
  • Oral surgery
  • Inflammation of the nerve
  • Cavernous sinus thrombosis
• Clinical features
  • Peripheral trigeminal nerve lesions
    • Ophthalmic nerve (V₁) is affected → absent corneal reflex (afferent limb), anesthesia of the forehead
    • Maxillary nerve (V₂) is affected; → anesthesia of the midface
    • Mandibular nerve (V₃) is affected → anesthesia of the chin, lower lip, and anterior two-thirds of the tongue; muscles of mastication are paralyzed
      • The jaw deviates towards the side of the lesion because of unopposed action from the opposite pterygoid muscle.
    • Involvement of any of the three branches can cause trigeminal neuralgia.
  • Lesion of the tensor tympani branch → hearing impairment (particularly difficulty hearing low-pitched sounds)
  • Lesions of the trigeminal nerve nuclei: Depending on which nuclei are affected; , the patient may present with ipsilateral weakness of muscles of mastication and/or ipsilateral loss of sensation.
  • Complete trigeminal nerve lesions are rare.

References:^[6]

• Etiology
  • Most common ocular cranial nerve palsy
  • Acquired
    • Trauma (e.g., at the superior orbital fissure)
    • Pseudotumor cerebri
    • Cavernous sinus thrombosis
    • Space-occupying lesion causing downward pressure (e.g., tumor)
    • Diabetic neuropathy
  • Congenital: Duane syndrome (A rare type of strabismus characterized by an impaired abduction and ptosis on adduction.)
• Clinical features
  • Horizontal diplopia that worsens when looking at distant objects
  • Esotropia: medial deviation of the affected eye at primary gaze
  • Inability to abduct the eye (affected individuals will rotate the head to look to the side)

References:^{[7][8] [9]}

• See facial nerve palsy.

• Etiology
  • Bacterial meningitis (most common cranial nerve palsy)
  • Lyme disease
  • Tumor (e.g., acoustic neuroma, neurofibromatosis type 2)
• Clinical features
  • Sensorineural hearing loss
  • Vertigo
  • Horizontal nystagmus: Movement of the head induces saccadic movement of the eye toward the opposite side the side of the lesion.
  • Motion sickness

References:^[10]

• Etiology: often unknown; may be associated with compression by a blood vessel
• Clinical features
  • Loss of the gag reflex (afferent limb)
  • Loss of the carotid sinus reflex
  • Flaccid paralysis of the soft palate → deviation of the uvula away from the lesion (similar to vagus nerve lesions)
  • Sensory loss over the soft palate, upper pharynx, and posterior third of the tongue (including loss of taste sensation)
  • Mild dysphagia
  • Glossopharyngeal neuralgia: throat and ear pain

Lesions that affect the glossopharyngeal nerve typically also affect the vagus nerve because the glossopharyngeal nerve exits the medulla above the vagus nerve.

• Etiology
  • Trauma
  • Diabetes
  • Inflammation
  • Aortic aneurysms
  • Tumors
• Clinical features
  • Loss of the gag reflex (efferent limb)
  • Flaccid paralysis of the soft palate → nasal speech and deviation of the uvula away from the lesion
  • Epiglottic paralysis → aspiration
  • Dysphagia
  • Features of vocal cord paralysis
    • Dysphonia (hoarseness)
    • The vocal cord assumes a paramedian position.
  • Dysfunction of vagal nerve in the stomach → features of gastroparesis (poor gastric emptying)

• Etiology: surgeries of the lateral cervical region, especially the posterior border of the sternocleidomastoid (e.g., resection of cervical lymph nodes)
• Clinical features
  • Paresis of the sternocleidomastoid muscle → weakness turning the head towards the contralateral side (the left SCM turns the head to the right)
  • Paresis of the trapezius muscle → weakness during elevation of the ipsilateral shoulder (→ shoulder drooping) and lateral winging of the scapula

• Etiology
  • Tumors
  • Trauma
• Clinical features
  • Atrophy and fasciculation of the tongue on the side of the lesion
  • The tongue deviates to the side of the lesion when protruded.

References:^{[11][12][13][14]}