Facial Nerve Palsy: Upper Motor Neuron vs Lower Motor Neuron Lesions
Critical Distinction and Initial Assessment
The single most important clinical distinction is forehead involvement: Lower Motor Neuron (LMN) lesions affect the entire ipsilateral face including the forehead, while Upper Motor Neuron (UMN) lesions spare the forehead due to bilateral cortical innervation of the upper facial muscles. 1
Immediate Diagnostic Algorithm
If forehead is spared (UMN pattern) + any limb weakness = acute stroke until proven otherwise and requires immediate stroke protocol activation. 2 This represents the highest mortality risk despite potential for spontaneous improvement 2.
If forehead is involved (LMN pattern) without limb weakness = peripheral facial palsy (Bell's palsy most common), but central causes must still be excluded if other neurological signs are present. 2, 3
Key Examination Findings to Distinguish Patterns
UMN Lesion (Central Cause):
- Forehead sparing - patient can wrinkle forehead and close eyes 1, 2
- Contralateral hemiparesis or hemisensory loss strongly suggests stroke 2
- Other cranial nerve involvement suggests brainstem pathology 3
- Dysarthria, ataxia, or gaze abnormalities indicate central lesion 3
LMN Lesion (Peripheral Cause):
- Complete ipsilateral facial weakness including forehead 1, 2
- Inability to wrinkle forehead, close eye, or raise eyebrow on affected side 1
- May have hyperacusis, taste disturbance, or ear pain 1
- Isolated finding without other neurological deficits in typical Bell's palsy 1
Critical Pitfall: LMN facial palsy can rarely result from brainstem stroke affecting the facial colliculus, presenting with isolated facial weakness initially but developing other signs (gaze palsy, ataxia) on repeat examination 3, 4. Any LMN facial palsy with additional neurological symptoms warrants urgent neuroimaging 3, 4.
Treatment Approach for LMN Lesions (Bell's Palsy)
Immediate Management (Within 72 Hours)
Oral corticosteroids are the cornerstone of treatment and must be initiated within 72 hours of symptom onset for maximum benefit. 1, 5
Recommended regimen:
- Prednisolone 50 mg daily for 10 days, OR 1
- Prednisone 60 mg daily for 5 days followed by 5-day taper 1
- Alternative: Prednisolone 25 mg twice daily for 10 days 5
Evidence supporting steroids: 83% recovery at 3 months with prednisolone vs 63.6% with placebo; 94.4% recovery at 9 months vs 81.6% with placebo (NNT = 10) 1, 5.
Antiviral therapy alone should NEVER be prescribed - it is ineffective as monotherapy 1, 2. Combination therapy with antivirals plus steroids may be offered as an option within 72 hours, showing marginally higher complete recovery rates (96.5% vs 89.7% with steroids alone), but the benefit is small 1.
Eye Protection Protocol (Mandatory for All Patients)
Implement comprehensive eye protection immediately to prevent corneal damage, which is the most serious acute complication. 1, 6
Stepwise eye protection algorithm:
Mild lagophthalmos (incomplete eye closure):
Moderate lagophthalmos:
Severe lagophthalmos (complete inability to close eye):
Warning signs requiring immediate ophthalmology referral: eye pain, vision changes, redness, discharge, foreign body sensation, or increasing irritation despite protection measures 1.
Critical pitfall: Improper eye taping technique can cause corneal abrasion - patients must receive careful instruction 1. Relying solely on drops without nighttime protection leads to exposure keratitis 1.
Diagnostic Testing
Routine laboratory testing and diagnostic imaging are NOT recommended for initial Bell's palsy diagnosis. 1, 6
Electrodiagnostic testing (ENoG and EMG) should be offered to patients with complete facial paralysis but NOT to those with incomplete paralysis. 1 Testing is most reliable when performed 3-14 days post-onset 1, 7.
MRI with and without contrast is indicated for:
- Atypical presentations (bilateral weakness, isolated branch paralysis, other cranial nerve involvement) 1, 2
- No recovery after 3 months 1, 2
- Worsening symptoms 1
- Second paralysis on same side 2
Follow-Up and Reassessment
Mandatory reassessment or specialist referral at 3 months if incomplete facial recovery. 1, 2
Immediate referral triggers at any time point:
- New or worsening neurological findings 1, 2
- Development of ocular symptoms 1, 2
- Signs of corneal exposure or damage 1
Prognosis
Patients with incomplete paralysis at presentation have excellent prognosis with up to 94% recovery rates. 1 Complete paralysis carries 70% recovery rate at 6 months 1, 5. Approximately 30% may experience permanent facial weakness with muscle contractures 1.
Electrodiagnostic prognostic indicators:
10% nerve response amplitude = excellent prognosis 1
- <10% function = up to 50% risk of incomplete recovery 1
Treatment Approach for UMN Lesions (Stroke)
UMN facial palsy from stroke requires immediate activation of stroke protocol - treatment focuses on the underlying cerebrovascular event, not the facial weakness itself. 2
Management priorities:
- Immediate CT/MRI brain to confirm stroke 2
- Thrombolysis or thrombectomy if within appropriate time window (per stroke guidelines) 2
- Admission to stroke unit 2
- Secondary stroke prevention 2
The facial weakness typically improves with stroke recovery and does not require specific facial nerve-directed therapy. 2 Eye protection is rarely needed as forehead function is preserved allowing eye closure 1, 2.
Special Populations
Traumatic Facial Nerve Palsy
CT temporal bone with thin sections is the primary imaging modality for traumatic facial palsy. 7 MRI with contrast should be obtained if CT is negative but clinical suspicion remains high 7.
Corticosteroids (prednisolone 1 mg/kg/day, maximum 50-60 mg daily) should be initiated within 72 hours if possible, though benefit may extend beyond this window in trauma. 7
Surgical decompression is indicated if ENoG shows >90% amplitude reduction compared to contralateral side. 7, 2 Surgery should be performed within 3-14 days of injury for optimal results 7, 2.
Pediatric Patients
Children have better prognosis than adults with higher rates of spontaneous recovery, but the benefit of corticosteroid treatment in children is inconclusive. 1 Treatment decisions should involve substantial caregiver participation in shared decision-making 1.
If treating, use prednisolone 1 mg/kg/day (maximum 50-60 mg) for 5 days followed by 5-day taper, though pediatric applicability is uncertain. 1
Pregnancy
Pregnant women with Bell's palsy should be treated with oral corticosteroids within 72 hours with careful individualized assessment of benefits and risks. 1 Eye protection measures are essential and safe in pregnancy 1.
Long-Term Management for Incomplete Recovery
Patients with incomplete recovery at 3 months require referral to facial nerve specialist for evaluation of reconstructive procedures. 1, 2
Reconstructive options include:
- Static procedures: eyelid weights, brow lifts, static facial slings 1, 2
- Dynamic procedures: nerve transfers, dynamic facial slings 1
- Tarsorrhaphy for persistent severe lagophthalmos 1, 6
Facial rehabilitation with neuromuscular reeducation, soft tissue mobilization, and chemodenervation improves facial muscle motor control, decreases synkinesis, and enhances quality of life. 9
Psychological support is critical - patients with persistent facial paralysis experience significant psychosocial dysfunction, difficulty expressing emotion, stigmatization, and elevated risk of depression requiring specialist referral 1.