Cranial Nerve Disorders
THIRD CRANIAL NERVE
PALSIES
Partial to complete weakness of the muscles
innervated by the 3rd (oculomotor) nerve,
resulting in ptosis of the lid, mydriasis, and an
outwardly turned eye during primary gaze.
 When the patient attempts to turn the eye inward,
it moves slowly only to the midline. Upward and
downward gaze is compromised in the affected
eye. When downward gaze is attempted, the
superior oblique muscle causes the eye to rotate
inward.
Causes of 3rd cranial nerve
palsies
 The many causes of 3rd cranial nerve palsies include
most major causes of CNS disease, so choice of
diagnostic tests should be based on the clinical features of
the palsy. Intraorbital structural lesions producing
external ophthalmoplegia and ocular myopathies should
be distinguished from cranial nerve disease.
Exophthalmos or enophthalmos, a history of severe
orbital trauma, or an obviously inflamed orbit suggests
restrictive orbital disease, which may impair ocular
motility. Myopathies are harder to diagnose but are
suggested by a partial 3rd nerve palsy. The pupil is
always spared in myopathy.
Causes of 3rd cranial nerve
palsies
 Completely nonfunctional parasympathetic fibers
(causing fixed dilated pupils) strongly suggest
oculomotor nerve compression. The most common causes
are aneurysm (especially of the posterior communicating
artery), trauma, and intracranial mass lesion. Oculomotor
paralysis in an increasingly unresponsive patient suggests
transtentorial herniation and is a major emergency. If the
pupil is completely spared but all other muscles
innervated by the 3rd nerve are affected (eg, diabetic 3rd
nerve paresis), the cause is likely to be an ischemic
process of the oculomotor nerve or the midbrain; a
demyelinating process is less likely. However, about 5%
of posterior communicating artery aneurysms causing
oculomotor paralysis spare the pupil.
Investigation
 Third cranial nerve palsies are most indicative of serious
disease when associated with severe headache or altered
consciousness.
 A thorough neurologic examination with CT or MRI is
performed. Lumbar puncture is reserved for suspected
subarachnoid hemorrhage when CT does not show blood.
Cerebral angiography must be performed if aneurysm
causing subarachnoid hemorrhage is strongly suspected
or when the pupil is clearly affected and no head trauma
serious enough to fracture the skull has occurred.
FOURTH CRANIAL NERVE PALSIES
 Weakness of the muscle innervated by the 4th (trochlear)
nerve (superior oblique muscle).
 These palsies are often difficult to detect because they
affect vertical eye position predominantly when the eye is
turned inward. The patient sees double images, one above
and slightly to the side of the other. However, by tilting
the head to the side opposite the palsied muscle, the
patient may achieve full or almost full ocular motility
without double vision.
FOURTH CRANIAL NERVE PALSIES
 There are few common identified causes of 4th cranial
nerve palsies; many are idiopathic. Closed head trauma
without skull fracture is a common cause of unilateral and
bilateral palsies; the few cases that occur often follow
motor cycle accidents. Aneurysms, tumors, and multiple
sclerosis are rare causes.
 Evaluation of 4th nerve palsies is similar to that of 3rd
nerve palsies. Usually, the diagnosis is obvious from the
history and physical examination. Oculomotor exercises
may help. Sometimes surgery is necessary to restore
concordant vision.
SIXTH CRANIAL NERVE PALSIES
 Weakness of the muscles innervated by the 6th
(abducens) nerve.
 The eye is turned inward; it moves outward sluggishly,
reaching the midline at most.
 Idiopathic cases are common, although many occur in
elderly or diabetic patients in whom small vessel disease
may be suspected. In idiopathic cases, no other cranial
nerves are involved, and improvement should occur
within 2 mo.
Causes
 One identifiable cause is compression of the 6th nerve in
the cavernous sinus by a tumor originating in the
nasopharynx. Typically, severe pain in the head and
anesthesia in the distribution of the first division of the
5th nerve also occur. Anything that causes the brain to
shift may stretch the 6th nerve because of the acute angle
it makes before entering Dorello's canal. Thus 6th nerve
palsies may be due to large brain tumors remote from the
nerve, to increased intracranial pressure, or to lumbar
puncture.
Causes
 Diabetic infarction is one of the more common
causes. Other causes include trauma of
insufficient force to cause a basilar skull fracture,
infections or tumors affecting the meninges,
Wernicke's encephalopathy, aneurysm, and
multiple sclerosis. In children without evidence
of increased intracranial pressure, these palsies
can result from respiratory infection and thus
may be recurrent.
SIXTH CRANIAL NERVE PALSIES
 Diagnosing complete 6th cranial nerve palsies is easy, but
determining their etiology can be more challenging.
Excluding increased intracranial pressure and
papilledema (by looking for retinal venous pulsations
during funduscopy) is important. MRI or CT can help
exclude intracranial mass lesions, hydrocephalus, and
direct nerve compression by lesions in the orbit,
cavernous sinus, and base of the skull. Lumbar puncture
determines the CSF opening pressure and can detect
leptomeningeal inflammatory, infectious, or neoplastic
infiltrates entrapping the 6th nerve. A collagen vascular
screen helps exclude a vasculopathic process. In many
cases, 6th nerve palsies resolve once the primary disorder
is treated.
TRIGEMINAL NEURALGIA
(Tic Douloureux)
 A disorder of the trigeminal nerve producing bouts of
excruciating, lancinating pain, lasting between seconds
and 2 min, along the distribution of one or more of its
sensory divisions, most often the maxillary.
 At surgery or autopsy, intracranial arterial and, less often,
venous loops compressing the trigeminal nerve root
where it enters the brain stem have been found,
suggesting that the tic is a compressive neuropathy. The
disorder usually affects adults, especially the elderly. Pain
is often set off by touching a trigger point or by activity
(eg, chewing or brushing the teeth). Although each bout
of intense pain is brief, successive bouts may be
incapacitating.
TRIGEMINAL NEURALGIA
(Tic Douloureux)
 Differential diagnosis includes neoplasm, vascular
malformation of the brain stem, a vascular insult, and
multiple sclerosis (especially in a younger patient).
Postherpetic pain is differentiated by its typical
antecedent rash, scarring, and predilection for the
ophthalmic division. Trigeminal neuropathy may occur in
Sjögren's syndrome or RA, but with a sensory deficit that
is often perioral and nasal. Migraine may produce
atypical facial pain, with normal examination results, but
the pain is more prolonged and is burning or throbbing.
FACIAL NERVE DISORDERS
 Unilateral facial weakness is a common
neurologic sign.
Bell's Palsy
 Unilateral facial paralysis of sudden onset and unknown cause.
 The mechanism presumably involves swelling of the nerve due to
immune or viral disease, with ischemia and compression of the facial
nerve in the narrow confines of its course through the temporal bone.
 Pain behind the ear may precede facial weakness. Weakness develops
within hours, sometimes to complete paralysis. The affected side
becomes flat and expressionless, but patients may complain instead
about the seemingly twisted intact side. In severe cases, the palpebral
fissure widens, and the eye does not close. The patient may complain
of a numb or heavy feeling in the face, but no sensory loss is
demonstrable. A proximal lesion may affect salivation, taste, and
lacrimation and may cause hyperacusis.
Diagnosis
 Weakness of the entire half of the face distinguishes Bell's palsy from
supranuclear lesions (eg, stroke, cerebral tumor), in which the
weakness is partial, affecting the frontalis and orbicularis oculi less
than the muscles in the lower part of the face. Bell's palsy must be
differentiated from unilateral facial weakness due to other disorders
of the facial nerve or its nucleus, chiefly geniculate herpes (Ramsay
Hunt's syndrome), middle ear or mastoid infections, sarcoidosis,
Lyme disease, petrous bone fractures, carcinomatous or leukemic
nerve invasion, chronic meningeal infections, and cerebellopontine
angle or glomus jugulare tumors. Skull x-rays and CT and MRI scans
are obtained when the diagnosis is in doubt. MRI may show contrast
enhancement of the facial nerve, but CT and skull x-rays are typically
negative. However, they may show a fracture line, bony erosion due
to infection or neoplasm, or internal auditory canal expansion due to
a cerebellopontine angle tumor. CT and MRI scans may show the
contrast-enhancing mass of angle or glomus tumors. Blood tests for
Lyme disease help diagnose it. A chest x-ray and serum ACE are used
to detect sarcoidosis, a common cause of facial nerve paralysis in
blacks.
Prognosis and Treatment
 The extent of nerve damage determines outcome; nerve conduction studies
and electromyography are useful. Complete recovery within several months
invariably follows acute partial paralysis. The likelihood of complete
recovery after total paralysis is 90% if the nerve branches in the face retain
normal excitability to supramaximal electrical stimulation but is only about
20% if electrical excitability is absent.
 Misdirected regrowth of nerve fibers may innervate lower facial muscles
with periocular fibers and vice versa, resulting in contraction of unexpected
muscles during voluntary facial movements (synkinesia) or "crocodile tears"
during salivation. Facial muscle contractures may follow chronic weakness.
 Measures must be taken to prevent corneal drying. They include frequent use
of natural tears, isotonic saline and methylcellulose drops, and strips of skin
tape to help close the eye. Supportive measures, such as temporary patching,
may suffice to protect the exposed eye; tarsorrhaphy may be needed when
palpebral fissure persists.
Corticosteroids
 Some studies suggest that corticosteroids (eg,
prednisone 60 to 80 mg/day po begun 24 to 48 h
after onset and given for 1 wk, then decreased
gradually over the 2nd wk) help modestly reduce
residual paralysis and expedite recovery. Mild
electrical stimulation of the nerve and massage of
the facial muscles have no proven benefit.
Hypoglossal-facial nerve anastomosis may
partially restore facial function if none has
returned in 6 to 12 mo but results in difficulty in
eating and speaking, so its role is limited.
GLOSSOPHARYNGEAL NEURALGIA
 A rare syndrome characterized by recurrent attacks of severe pain in
the posterior pharynx, tonsils, back of the tongue, and middle ear.
 The cause is unknown, and no pathologic change can be found
(except rarely, when due to a tumor in the cerebellopontine angle or
the neck). Men are more commonly affected, usually after age 40.
 As in trigeminal neuralgia, intermittent attacks of brief, severe,
excruciating pain occur paroxysmally, either spontaneously or
precipitated by movement (eg, chewing, swallowing, talking,
sneezing). The pain, lasting seconds to a few minutes, usually begins
in the tonsillar region or at the base of the tongue and may radiate to
the ipsilateral ear. The pain is strictly unilateral. In 1 to 2% of
patients, increased vagus nerve activity causes cardiac sinus arrest
with syncope. Attacks may be separated by long intervals.
Diagnosis and Treatment
 Location of the pain, precipitation of an attack by swallowing or by
touching the tonsils with an applicator, and temporary elimination of
pain with lidocaine applied locally to the throat (after which the pain
cannot be evoked by stimulation) distinguish glossopharyngeal
neuralgia from trigeminal neuralgia of the mandibular division.
Tonsillar, pharyngeal, and cerebellopontine angle tumors and
metastatic lesions in the anterior cervical triangle must be ruled out
by brain imaging.
 Carbamazepine is the drug of choice. Phenytoin, baclofen, or
amitriptyline in doses as for trigeminal neuralgia (see above ) or
trazodone 150 to 400 mg/day in 3 divided doses may be added if
necessary. If they are ineffective, cocainization of the pharynx may
provide temporary relief, and surgery may be necessary. When pain is
restricted to the pharynx, the nerve in the neck may be avulsed; it
must be sectioned intracranially if pain is widespread.