What are the causes and management of recurrent Lower Motor Neuron (LMN) facial nerve palsy?

Causes and Management of Recurrent Lower Motor Neuron Facial Nerve Palsy

Recurrent lower motor neuron (LMN) facial nerve palsy requires thorough investigation as it is rarely idiopathic, with approximately 77% of cases ultimately diagnosed as idiopathic after extensive workup. 1

Causes of Recurrent LMN Facial Nerve Palsy

Common Causes

• Idiopathic (Bell's palsy): Most common diagnosis (77.4% of cases) after exclusion of other causes 1
• Melkersson-Rosenthal syndrome: Accounts for 7.5% of recurrent cases 1
• Neoplastic causes: 5.7% of cases, including:
  • Facial nerve schwannoma (3.7%)
  • Metastatic squamous cell carcinoma to parotid (1.9%) 1
• Neurosarcoidosis: 3.7% of cases 1
• Infectious causes:
  • Herpes zoster (Ramsay Hunt syndrome) (1.9%) 1
  • Lyme disease (in endemic areas) 2

Less Common Causes

• Autoimmune disorders: Granulomatosis with polyangiitis (1.9%) 1
• Traumatic neuroma: 1.9% of cases 1
• Metabolic disorders:
  • Diabetes mellitus 3
  • Hypovitaminosis A (particularly in children) 4
• Vascular causes:
  • Pontine infarction (facial colliculus syndrome) 5

Diagnostic Approach

Initial Evaluation

• Document timing, frequency, and side of recurrences (ipsilateral vs. contralateral) 1
• Assess for associated symptoms that suggest central causes:
  • Vertigo, gait instability, nystagmus 5
  • Dizziness, dysphagia, diplopia 2
• Evaluate for risk factors:
  • History of skin cancers on head/face
  • Parotid tumors
  • Head/facial trauma
  • Recent infections 2

Laboratory Testing

• Targeted laboratory testing based on clinical suspicion:
  • Lyme disease serology (in endemic areas) 2
  • Inflammatory markers (ESR, CRP) for autoimmune conditions
  • Vitamin A levels if deficiency suspected 4

Imaging

• MRI head with and without contrast: First-line imaging modality for recurrent facial palsy 2, 6

  • High-resolution thin-cut sequences through the course of CN VII
  • Evaluate brainstem, cerebellopontine angle, internal auditory canal, and temporal bone
  • Particularly important if symptoms persist beyond 2-4 months 2

• CT temporal bone: Complementary to MRI for evaluating osseous integrity of temporal bone 2

Management Approach

Acute Management

1. Corticosteroids: Start within 72 hours of symptom onset

   • Prednisone 60-80mg daily for 7 days followed by taper 6
   • Improves recovery rates from 70% to 94% 6

2. Antiviral therapy: Optional addition to steroids

   • Valacyclovir 1g three times daily for 7 days OR
   • Acyclovir 400mg five times daily for 10 days 6
   • Note: Antiviral therapy alone is not effective 6

3. Ocular protection: Mandatory for patients with impaired eye closure

   • Artificial tears, lubricating ointments
   • Eye patches or adhesive tape
   • Humid chambers, sunglasses for daytime protection 6

Management of Underlying Causes

• Neoplastic causes: Surgical resection or radiation therapy based on tumor type
• Infectious causes: Appropriate antimicrobial therapy
• Autoimmune disorders: Immunosuppressive therapy
• Metabolic disorders: Correction of deficiencies (e.g., vitamin A supplementation) 4

Surgical Considerations

• Facial nerve decompression: Consider in select cases of recurrent palsy
  • Middle cranial fossa approach has shown benefit in preventing subsequent episodes 1
• Reconstructive procedures for incomplete recovery:
  • Eyelid weights
  • Brow lifts
  • Static and dynamic facial slings 6

Follow-up and Monitoring

• Quantify facial nerve function using House-Brackmann scale (grades 1-6) 6
• Reevaluate if:
  • New or worsening neurological findings
  • Ocular symptoms persist
  • Incomplete facial recovery after 3 months 6

Referral Considerations

• Facial nerve specialist: For incomplete recovery after 3 months
• Neurologist: For new or worsening neurological findings
• Ophthalmologist: For persistent ocular symptoms 6
• Psychological support: For patients with persistent facial weakness experiencing social or emotional difficulties 6

Prognosis

• Overall prognosis varies based on underlying cause
• Idiopathic recurrent facial palsy: Generally good with appropriate treatment
• Median recovery to House-Brackmann grade 1.5 over approximately 62 days (range 1-420 days) 1
• Neoplastic causes: Prognosis depends on tumor type and extent