CRANIAL NERVE AND SENSORY EXAMINATION
1. THE OLFACTORY NERVES
Test this with odorous things, one nostril at a time.use coffee bean or citrus fruits , the
screening exam usually omits the first cranial nerve.
Common causes of cranial nerve I dysfunction include:
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trauma to the cribriform plate
frontal lobe mass or stroke
nasal problems (e.g. allergic or viral).
2. CRANIAL NERVE II: THE OPTIC NERVE
Test this with field of vision and visual acuity. To screen field of vision, test by
confrontation (patient looks at your nose while you move fingers).
Common causes of optic nerve abnormalities:
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Eye disease or injury. Diabetic retinopathy and glaucoma are major causes.
Occipital lobe mass or stroke. This causes loss of visual field in both eyes.
Patients can lose ½ or ¼ of a visual field
Optic chiasm mass, such as pituitary tumors. These cause loss of the temporal
visual fields bilaterally - bitemporal hemianopsia.
3. CRANIAL NERVE III, IV and VI: THE OCULOMOTOR, TROCHLEAR
and ABDUCENS NERVES
Test these three nerves with extraocular movements and pupil function (cranial nerve
III). To detect subtle abnormalities, ask patient whether they have double vision
(diplopia) during extraocular movements.
One mnemonic to remember these three nerves is LR6SO4 : all the muscles are
innervated by CN III except for the lateral rectus (6) and superior oblique (4).
Some common causes for cranial nerve palsies are:
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brainstem injury or compression (e.g. tumor, stroke, intracranial bleeding
diabetic neuropathy (can cause temporary palsies).
4. ABNORMALITIES of PUPIL RESPONSE and EXTRAOCULAR
MOVEMENTS
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Central nervous system syphilis produces an Argyll Robertson pupil (CN III) loss of pupil response to light, though the pupil still responds to
accommodation.
The mnemonic to remember the pupil change of syphilis is: it's like a sex
worker. It accommodates, but it doesn't respond.
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Lesions in any of these three nerves can cause abnormal extraocular
movements. Here are two examples - the first patient has an abnormality of
CN VI, the second an abnormality of CN III:
5. CRANIAL NERVE V: THE TRIGEMINAL NERVE
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Screen this nerve with facial sensation (to light touch, e.g. q-tip) and strength
of the masseter muscles.
Common cause for CN V abnormality is stroke in the contralateral sensory
cortex.
6. CRANIAL NERVE VII: THE FACIAL NERVE
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Test this with facial movements: ask the patient to raise eyebrows, show teeth,
smile, puff out cheeks, whistle.
Injuries to facial strength central to the nucleus (in the cortex or corticospinal
tracts) - often caused by a stroke - cause weakness of the lower face, with
sparing of the forehead, due to cross-innervation of the forehead. We call this
a central facial palsy.
Injuries to the facial nerve itself (peripheral facial palsy) cause weakness of
the entire side of the face, including the forehead. Common causes of
peripheral facial palsy are Bell's palsy (idiopathic - cause is unknown) and
Lyme disease (which may cause bilateral peripheral facial palsy).
7. CRANIAL NERVE VIII: THE ACOUSTIC NERVE
Test the acoustic nerve with hearing test (rub fingers by each ear, or whisper into ear,
or use your tuning fork). We do this as part of the ear examination. In patients with
vertigo or dizziness, you may test also with positional maneuvers, trying to reproduce
vertigo by moving the patient.
Common causes of acoustic nerve abnormalities:
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sensorineural hearing loss due to age or noise exposure
tumors at cerebellopontine angle
acoustic neuroma
earwax or middle ear disease can cause temporary hearing loss.
8. CRANIAL NERVE IX and X: THE GLOSSOPHARINGEAL and
VAGUS NERVES
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Test this with the gag reflex - put tongue blade on the posterior third of
patient's tongue and press down. Many clinicians prefer to have alert patient
phonate (say aaah) instead, watching for uvula movement.
A common cause of CN IX and X abnormality is a large stroke. The uvula
retracts to the normal side.
9. CRANIAL NERVE XI: THE ACCESSORY NERVE
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Test this nerve by asking patient to shrug shoulders or turn head against
resistance.
A common cause of CN XI abnormality is neck injury.
10. CRANIAL NERVE XII: THE HYPOGLOSSAL NERVE
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Test this nerve by asking patient to protrude tongue and move it from side to
side.
CN XII function abnormalities are often caused by stroke. The tongue points
toward its weak side.
SENSORY EXAMINATION
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Touch: Test light touch with a cotton swab or microfilament.
Subtle abnormality in touch sensation may manifest as extinction : with eyes
closed, the patient touched on both sides only feels touch on the normal side.
Sharp: Break off the wooden part of a cotton swab to make a sharp object.
Ask the patient with eyes closed to distinguish sharp from dull.
Vibration: test with low-frequency (128) tuning fork.
Proprioception: with eyes closed, patient distinguishes whether finger and toe
are moved up or down. This tests posterior column function.
SPECIAL TESTS of SENSORY FUNCTION
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These are not part of the basic screening examination and are included for
your information.
Stereognosis: with eyes closed, patient identifies pen, paper clip or coin
placed in hand. This tests the parietal sensory cortex and posterior columns
Graphesthesia: with eyes closed, patient identifies numbers written on palm.
This tests the sensory cortex and integration.
Two-point discrimination: patients should be able to distinguish points 2 to
10 mm apart on fingers and hands. This can be up to 75 mm on thigh and
back. Compare patient's two sides.