What is an effective method to assess cranial nerves II–XII in a primary‑care focused neurological examination?

Effective Primary Care Assessment of Cranial Nerves II–XII

In primary care, perform a dementia-focused elemental neurologic examination that efficiently screens for abnormalities of cranial nerve function, somatosensory or motor function, and postural/gait abnormalities, using a systematic approach that tests each nerve's specific function. 1

Systematic Approach to Cranial Nerve Examination

CN II (Optic Nerve): Visual Function

• Test visual acuity using a Snellen chart or near card 1
• Assess visual fields by confrontation testing in all four quadrants 1
• Examine pupillary light reflexes (direct and consensual) 1
• Perform fundoscopic examination to visualize the optic disc 1

Common pitfall: Visual loss from cataracts, macular degeneration, or glaucoma does not require neurological imaging, so distinguish these from true optic nerve pathology 1

CN III, IV, VI (Oculomotor, Trochlear, Abducens): Eye Movements

• Observe for ptosis and pupil size asymmetry at rest 1
• Test extraocular movements in all six cardinal directions of gaze (H-pattern) 1
• Check for diplopia in each gaze position 1
• Assess pupillary constriction to light and accommodation 1

Critical distinction: Pupil-involving third nerve palsy suggests external compression (potentially aneurysm), while pupil-sparing palsy suggests vasculopathic causes 1

CN V (Trigeminal Nerve): Facial Sensation and Jaw Function

• Test light touch and pinprick sensation in all three divisions (V1-ophthalmic, V2-maxillary, V3-mandibular) bilaterally 1
• Assess corneal reflex by lightly touching the cornea with a cotton wisp 1
• Test jaw strength by having the patient clench teeth and resist jaw opening 1
• Palpate masseter and temporalis muscles during clenching 1

CN VII (Facial Nerve): Facial Movement and Taste

• Observe facial symmetry at rest and during spontaneous expressions 1
• Test upper face: ask patient to raise eyebrows and close eyes tightly against resistance 1
• Test lower face: ask patient to smile, show teeth, and puff out cheeks 1
• Assess taste on anterior two-thirds of tongue using sweet, salty, sour, or bitter substances if indicated 2

Key distinction: Upper motor neuron lesions spare forehead movement due to bilateral innervation, while lower motor neuron lesions affect the entire ipsilateral face 1

CN VIII (Vestibulocochlear Nerve): Hearing and Balance

• Perform whisper test or finger rub test at arm's length from each ear 1
• Use Weber test (tuning fork on forehead midline) to detect lateralization 1
• Perform Rinne test (tuning fork on mastoid then near ear canal) to compare air versus bone conduction 1
• Observe for nystagmus and assess balance if vertigo is present 1

CN IX and X (Glossopharyngeal and Vagus): Pharyngeal Function

These nerves are tested together due to their overlapping functions 2, 3

• Observe palatal elevation by having patient say "ah" - the soft palate should elevate symmetrically and uvula should remain midline 2, 3
• With unilateral vagal palsy, the uvula deviates toward the intact side due to unopposed muscle contraction 2, 3
• Test gag reflex by touching posterior pharyngeal wall bilaterally 2
• Assess voice quality for hoarseness, breathy quality, or nasal speech suggesting vocal cord paralysis 2
• Ask patient to cough forcefully - a weak, ineffective cough suggests vocal cord weakness 2
• Test taste on posterior one-third of tongue if CN IX dysfunction suspected 2

Anatomical consideration: The affected side of the palate appears lower and moves less than the normal side during phonation 2

CN XI (Accessory Nerve): Shoulder and Neck Strength

• Inspect for visible atrophy or asymmetry of trapezius muscles and shoulder drooping 4
• Palpate upper trapezius muscles along shoulder girdle to detect atrophy or fasciculations 4
• Test shoulder shrug: ask patient to elevate shoulders upward against downward pressure from your hands 4
• Test sternocleidomastoid strength: ask patient to turn head against resistance while palpating the contralateral SCM 4

CN XII (Hypoglossal Nerve): Tongue Movement

• Observe tongue at rest in the mouth for atrophy or fasciculations 3
• Ask patient to protrude tongue - it deviates toward the side of the lesion 3
• Test tongue strength by having patient push tongue against cheek while you apply external resistance 3
• Assess tongue movements side-to-side and up-and-down 3

Clinical Decision-Making After Examination

If abnormalities are identified on neurologic examination, referral to a specialist is warranted if the primary care clinician is unsure about interpretation or implications 1

When to Consider Imaging

• Multiple ipsilateral cranial nerve palsies suggest cavernous sinus, orbital apex, or basilar subarachnoid pathology 1
• Brainstem lesions affecting nucleus ambiguus cause ipsilateral palatal weakness with associated brainstem signs 2
• Peripheral lesions at jugular foramen typically involve CN IX, X, and XI together 2
• Any confirmed CN IX or X deficit requires contrast-enhanced MRI 2, 3

Safety Considerations

Abnormalities on neurologic exam may raise questions about potential safety risks including falls, aspiration, and driving ability 1

Practical Efficiency Tips

The entire cranial nerve examination can be completed efficiently within a problem-focused visit by:

• Integrating tests into natural conversation (observing facial symmetry, voice quality, eye movements during history-taking) 1
• Grouping related functions (testing CN III, IV, VI together during eye movement assessment) 1
• Focusing on high-yield tests when time is limited (pupillary reflexes, facial symmetry, palatal elevation, tongue protrusion) 1, 2

This examination requires no complicated or potentially unavailable equipment and can be performed quickly and efficiently in primary care 5