Facial-nerve palsy localisation

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

The facial nerve supplies muscles of facial expression and carries additional taste and parasympathetic fibres. A useful localisation begins with the distribution of motor weakness, then incorporates accompanying neurological, auditory and autonomic symptoms. Ask the patient to raise the eyebrows, close the eyes, show the teeth and puff out the cheeks. Inspect at rest and during movement, because subtle weakness and synkinesis may be missed by a single smile test.

Supranuclear lesions often weaken the opposite lower face more than the forehead because upper facial motor control receives bilateral cortical input. A lesion at the facial nucleus in the pons or along the outgoing nerve can weaken the entire same-side face. This distinction describes a motor pattern rather than a complete diagnosis. The tempo, other cranial nerves, limb findings and local ear or parotid abnormalities determine whether the cause is stroke, inflammation, infection, trauma or a structural lesion.

Key points

Compare forehead movement, gentle and forceful eye closure, smile and lip seal.
Relative forehead sparing suggests a supranuclear lesion but is not an absolute rule.
Whole-face weakness can arise in the facial nucleus, fascicle or peripheral nerve.
Examine ears, palate, parotid region and the other cranial nerves.
Bell palsy is an acute isolated idiopathic lower motor neurone facial palsy.
Start appropriate Bell palsy steroids within seventy-two hours when indicated.
Eye protection begins at presentation and continues until closure is adequate.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Supranuclear or brainstem disease

Stroke, demyelination and structural lesions can affect descending facial pathways or the pontine nucleus and fascicle, producing different motor patterns and associated neurological signs.

Peripheral facial nerve disease

Idiopathic inflammation, VZV, Lyme disease, middle-ear pathology, parotid lesions and trauma can injure the nerve at different points along its course.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Bilateral upper facial input
Bilateral corticobulbar input to upper facial motor control often preserves forehead movement after a unilateral supranuclear lesion, while the opposite lower face weakens.
2
Final motor pathway injury
Injury to the facial nucleus or its axons interrupts the shared output to upper and lower facial muscles on the same side.
3
Loss of eyelid protection
Weak orbicularis oculi reduces blink and closure, allowing tear-film disruption and corneal exposure even when tear production remains present or the eye waters.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Supranuclear pattern

Relative preservation of forehead movement with contralateral lower facial weakness supports a supranuclear lesion, particularly with arm weakness or language disturbance. Sudden onset requires a stroke assessment. Do not expect every central lesion to follow a perfectly textbook distribution.

Nuclear or fascicular involvement

A pontine lesion may cause complete ipsilateral facial weakness with horizontal gaze disturbance, other cranial nerve signs or contralateral limb findings. Original stroke case series demonstrate this peripheral-looking pattern. Forehead involvement must therefore be interpreted with the full neurological examination.

Peripheral nerve clues

Hyperacusis may reflect stapedius involvement, altered anterior tongue taste may reflect chorda tympani involvement, and tear symptoms can accompany more proximal disease. These clues are supportive rather than exact bedside coordinates; subjective tearing can also result from impaired eyelid mechanics.

Ear, skin and parotid assessment

Look for ear-canal or palatal vesicles, otitis, mastoid changes, trauma scars and a parotid mass. Severe otalgia and vesicles suggest Ramsay Hunt syndrome. Ask about tick exposure, an expanding rash and systemic features when considering Lyme disease.

Corneal protection

Assess blink, eyelid closure, ocular surface symptoms and vision. A watering eye may still have exposure. Reduced corneal sensation adds risk because significant injury can produce surprisingly little pain. Inability to protect the cornea warrants ophthalmic involvement.

Red flags requiring action

Facial weakness with diplopia, gaze disturbance, dysarthria, limb findings or severe ataxia needs urgent assessment for a central lesion.
Painful red eye, reduced vision or inadequate corneal protection in facial palsy requires urgent ophthalmic assessment.
Progressive, recurrent same-sided, bilateral or otherwise atypical facial weakness requires investigation rather than an automatic Bell palsy label.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Structured bedside localisationFirst step
Why
Determine whether facial weakness is isolated and identify an urgent central pattern.
Interpretation and limitations
Document each facial movement, eye closure, pupils, ocular movements, hearing and other cranial nerves, alongside limb examination and gait. A whole-face pattern with gaze disturbance is not uncomplicated Bell palsy. Record severity with a recognised scale when useful for follow-up.
02
Eye assessment
Why
Identify exposure and establish whether lubrication and closure support are sufficient.
Interpretation and limitations
Check visual acuity and the ocular surface; fluorescein assessment may reveal epithelial injury when performed by a competent clinician. Arrange urgent ophthalmic review for pain, redness, reduced vision or inadequate protection rather than relying on a patch alone.
03
Selective infection testing
Why
Investigate a specific infectious explanation supported by history or examination.
Interpretation and limitations
Consider Lyme serology according to exposure and regional pathways, recognising that early negative testing may need follow-up. NHS Highland uses a more proactive approach because local risk is higher. Vesicle PCR can support VZV diagnosis but should not delay appropriate early treatment.
04
Directed imaging and specialist assessment
Why
Investigate central, structural, traumatic or atypical facial palsy.
Interpretation and limitations
Acute central concern follows emergency imaging pathways. Progressive weakness, recurrence on the same side, multiple cranial nerves, trauma or a parotid lesion may require targeted brain, temporal-bone or parotid imaging. Uncomplicated isolated Bell palsy does not routinely require imaging or specialist referral.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Ramsay Hunt syndrome

VZV-associated facial palsy may include severe otalgia, ear or oral vesicles and auditory or vestibular symptoms, requiring prompt antiviral and specialist consideration.

Lyme neuroborreliosis

Facial palsy can follow tick exposure and may be bilateral or accompanied by radicular pain or other systemic features that guide infection assessment.

Parotid or skull-base lesion

Gradually progressive or recurrent weakness, a palpable mass or multiple cranial nerve findings raises concern for structural disease along the facial nerve pathway.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01UrgentCentral or ocular dangerFirst stepNew facial weakness has associated neurological findings or threatened corneal protection.

1Activate the stroke pathway when sudden neurological features suggest a cerebral or brainstem event, documenting onset and associated deficits.
2Begin ocular lubrication and safe closure support when needed while obtaining urgent ophthalmic advice for an unprotected or symptomatic cornea.
3Arrange immediate ENT assessment for acquired unilateral hearing loss with same-sided facial weakness, or use stroke referral when that diagnosis is suspected.

02TypicalSupported uncomplicated Bell palsyAn acute unilateral lower motor neurone facial palsy remains isolated after appropriate assessment.

1Explain the working diagnosis and expected gradual recovery, while giving clear advice about new neurological, auditory or ocular symptoms.
2Consider a supported oral prednisolone regimen within seventy-two hours, checking important comorbidities and medication risks.
3Teach eye care and safe night-time closure support, ensure the patient can perform it and arrange a practical review.
4Avoid routine antiviral treatment for uncomplicated idiopathic Bell palsy; vesicles or other evidence of VZV changes the diagnosis and treatment plan.

03AtypicalInvestigate another cause or incomplete recoveryThe course, examination or subsequent progress is inconsistent with an uncomplicated episode.

1Refer progressive, bilateral, recurrent or multi-nerve weakness for specialist investigation rather than repeating empirical treatment without explanation.
2Review persistent deficits, eye protection, eating and speech, and consider facial rehabilitation or specialist facial nerve services.
3For aberrant reinnervation persisting at least five months after Bell palsy onset, NICE advises considering neurological referral for assessment and possible treatment.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Improves the chance of recovery in an acute idiopathic Bell palsy when given early after assessment.

Prednisolone for an appropriately diagnosed Bell palsy

The NHS Highland adult regimen is 60 mg orally once daily for five days, then 50 mg on day six, 40 mg on day seven, 30 mg on day eight, 20 mg on day nine and 10 mg on day ten, then stop. Start within seventy-two hours when indicated.

Seek specific advice with pregnancy, diabetes, glaucoma, active infection or peptic ulcer disease. Discuss glucose changes, mood disturbance and sleep effects, and account for existing steroid treatment. This regimen is for Bell palsy and should not be applied automatically to facial weakness of another cause.

Provides a lubricating barrier to reduce ocular surface drying when eyelid function is impaired.

Simple Eye Ointment BP, product 3538

Place a thin line inside the lower eyelid as required; night-time application can supplement daytime lubrication in an agreed eye-protection plan. Continue protection until blink and closure are adequate, with earlier reassessment for ocular symptoms. Discard the opened tube after one month.

Avoid with ingredient hypersensitivity, including sensitivity to lanolin. Do not wear contact lenses during treatment or touch the nozzle to the eye. Blurring is expected after application; driving must wait until vision is clear. Ointment alone may be insufficient for substantial exposure.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Exposure keratopathy

An inadequately protected ocular surface can develop epithelial injury, infection and visual impairment. Reduced corneal sensation may make the degree of discomfort misleading.

Oral and speech difficulty

Reduced lip seal and cheek tone can cause drooling, food trapping and difficulty articulating sounds, affecting nutrition, communication and confidence.

Synkinesis and residual asymmetry

Incomplete or aberrant recovery can leave persistent weakness or involuntary linked movements, requiring assessment of function and targeted rehabilitation rather than appearance alone.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Review eye comfort, visual symptoms and the ability to close the eyelid, confirming that the patient or carer can apply the agreed protection correctly.
Record facial recovery using comparable movements and severity grading rather than an unqualified improving or unchanged entry.
Ask about eating, drinking, speech, social confidence and abnormal linked movements, which may need rehabilitation even when resting symmetry improves.
Reassess the diagnosis if additional symptoms emerge or recovery is unexpectedly poor; a previous Bell palsy label should not block appropriate imaging or specialist referral.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Corneal reflex anatomy

The sensory limb of the corneal reflex travels mainly through the ophthalmic trigeminal division, while the blink response depends on the facial nerve. Combined sensory loss and facial weakness can increase exposure risk and may suggest a lesion involving neighbouring structures.

Eye taping needs demonstration

Night-time taping should keep the eyelid gently closed without pressure on the globe or allowing the tape to contact the ocular surface. Demonstrate the technique and check closure. An eye patch over an open eye is not reliable protection.

Regional infection probability

Lyme risk varies with geography and exposure. The NHS Highland recommendation to investigate broadly reflects local epidemiology and should be understood as a regional pathway, while a compatible exposure or systemic presentation elsewhere still warrants investigation.

Recovery and synkinesis

Facial movement may return unevenly over months. Aberrant reinnervation can produce involuntary eye closure with mouth movement or other linked activity. Specialist facial therapy can address functional problems; forceful unsupervised exercise is not a substitute for assessment.

11Common pitfallsFrequent interpretation and management errors.

01
Equating whole-face weakness with a proven extracranial lesion ignores the facial nucleus and fascicle within the pons.
02
Calling facial palsy idiopathic before examining the ear canal, palate and parotid region can miss infection or a structural cause.
03
Providing a steroid prescription without an eye-protection plan neglects an immediate preventable complication.
04
Repeating the same treatment for progressive or recurrent weakness without reviewing the diagnosis may delay identification of a tumour or systemic disorder.