What is the approach to examining a patient with suspected seventh cranial nerve dysfunction, including symptoms of facial weakness, changes in taste, or difficulty speaking?

Examination of the Seventh Cranial Nerve (Facial Nerve)

Begin by systematically testing facial muscle strength, asking the patient to raise eyebrows, close eyes tightly, smile, and puff out cheeks, while simultaneously assessing for taste disturbance in the anterior two-thirds of the tongue and checking for hyperacusis. 1

Motor Function Assessment

The facial nerve (CN VII) provides branchial motor innervation to all muscles of facial expression, and complete testing requires evaluation of both upper and lower facial muscles. 1

Upper Face Testing

• Ask the patient to raise both eyebrows and wrinkle the forehead - inability to do so on one side indicates a lower motor neuron lesion affecting CN VII, whereas preserved forehead function with lower face weakness suggests an upper motor neuron (central) lesion 2, 3
• Test eye closure by asking the patient to close eyes tightly while you attempt to open them - incomplete closure indicates facial nerve weakness and puts the patient at risk for corneal injury 1, 4
• Document any asymmetry at rest, including drooping of the upper eyelid or flattening of the nasolabial fold 4

Lower Face Testing

• Ask the patient to smile broadly and show teeth - observe for asymmetry with the mouth pulling only toward the unaffected side 4
• Have the patient puff out both cheeks - weakness allows air to escape on the affected side 5
• Ask the patient to purse lips tightly - inability indicates orbicularis oris weakness 2

Special Sensory Function (Taste)

Test taste sensation on the anterior two-thirds of the tongue using sweet, salty, or sour substances applied to each side separately, as the facial nerve carries special sensory fibers through the chorda tympani branch 1, 4. Taste disturbance (dysgeusia) commonly accompanies facial nerve lesions proximal to the chorda tympani branch 5, 2.

Additional Associated Symptoms

Specifically inquire about and test for:

• Hyperacusis (increased sensitivity to sound) - indicates involvement of the nerve to stapedius muscle 1, 5, 2
• Dry eye or excessive tearing - reflects parasympathetic dysfunction 1, 4
• Ipsilateral ear or facial pain - common presenting symptom in Bell's palsy 4
• Onset timing - Bell's palsy characteristically develops within 72 hours 4

Severity Grading

Use the House-Brackmann grading system to document severity: 4

• Grade 1: No visible weakness
• Grade 2: Slight weakness with normal symmetry at rest
• Grade 3: Obvious asymmetry but not disfiguring, slight forehead movement, incomplete eye closure with effort
• Grade 4: Disfiguring asymmetry, no forehead movement, incomplete eye closure
• Grade 5: Barely perceptible motion, incomplete eye closure even with maximal effort
• Grade 6: Complete paralysis with no movement

Critical Red Flags Requiring Further Evaluation

The following findings indicate the facial weakness is NOT simple Bell's palsy and mandate imaging: 4, 2, 3

• Any other cranial nerve involvement (especially CN V, VI, VIII, IX, X, XI, or XII) - suggests central pathology or skull base lesion 1, 4, 3
• Bilateral facial weakness - consider Lyme disease, sarcoidosis, or Guillain-Barré syndrome 4, 2
• Gradual onset over weeks - suggests tumor rather than Bell's palsy 4
• Associated vertigo, ataxia, or gaze palsy - indicates brainstem pathology such as facial colliculus syndrome 3
• Limb weakness, speech difficulties, or altered mental status - suggests stroke 4
• Symptoms persisting beyond 2 months - requires MRI evaluation 1

Imaging Indications

For typical Bell's palsy presentation (isolated LMN facial weakness developing within 72 hours), no imaging is required. 4 However, MRI of the orbit, face, and neck with and without IV contrast (rating 9/9) combined with MRI head with and without IV contrast (rating 8/9) is the gold standard when imaging is indicated. 1

When to Image:

• Atypical presentation or symptoms persisting >2 months 1, 4
• Any additional neurological findings 4, 3
• Suspected tumor, trauma, or other structural lesion 1
• Hemifacial spasm or recurrent facial paralysis 1

CT of the temporal bone with thin sections is complementary for evaluating fractures, osseous anatomy, and middle ear disease, but MRI remains the primary modality. 1

Common Pitfalls to Avoid

• Do not assume all unilateral facial weakness is peripheral - always test forehead function to distinguish upper from lower motor neuron lesions 2, 3
• Do not overlook eye protection - implement lubricating drops, ointment, and eye taping immediately to prevent permanent corneal damage in any patient with incomplete eye closure 4, 2
• Do not miss evolving neurological signs - if symptoms do not improve with initial treatment or new symptoms develop, repeat the neurological examination 3
• Do not forget to examine all other cranial nerves - involvement of multiple cranial nerves excludes Bell's palsy and indicates serious pathology requiring urgent imaging 1, 4