What is the most common cause of facial nerve paralysis?

Bell's Palsy is the Most Common Cause of Facial Nerve Paralysis

Bell's palsy is the most common cause of facial nerve paralysis. 1, 2

Epidemiology and Definition

• Bell's palsy is the most common acute mono-neuropathy affecting the facial nerve, and the most common diagnosis associated with facial nerve weakness/paralysis 1
• It is defined as acute unilateral facial nerve paresis (weakness) or paralysis (complete loss of movement) with onset in less than 72 hours and without an identifiable cause 2, 3
• Bell's palsy can affect men, women, and children, but is more common in those 15 to 45 years old, with higher incidence in patients with diabetes, upper respiratory ailments, compromised immune systems, and during pregnancy 2

Differential Diagnosis

• While Bell's palsy is the most common cause, other conditions that may cause facial paralysis include:
  • Stroke
  • Brain tumors
  • Tumors of the parotid gland or infratemporal fossa
  • Cancer involving the facial nerve
  • Systemic and infectious diseases including Herpes zoster and Lyme disease
  • Trauma (including faciomaxillary injuries)
  • Iatrogenic causes (such as parotid surgery) 1, 2

Clinical Presentation

• Bell's palsy presents with rapid onset of unilateral facial weakness or paralysis involving the forehead 3
• Symptoms may include:
  • Inability to close the eyelid
  • Oral incompetence
  • Dryness of the eye or mouth
  • Taste disturbance
  • Hyperacusis
  • Sagging of the eyelid or corner of the mouth 2

Diagnosis

• Bell's palsy is diagnosed by exclusion, with careful elimination of other causes 2
• Red flags requiring further investigation include:
  • Advanced age
  • Bilateral facial weakness
  • New or worsening neurologic findings 2
• Routine laboratory testing and diagnostic imaging are NOT recommended for initial Bell's palsy diagnosis 3
• MRI with contrast is the imaging test of choice when indicated (for atypical presentations, no recovery after 3 months, or worsening symptoms) 3

Treatment

• Oral corticosteroids should be prescribed within 72 hours of symptom onset for patients 16 years and older 3
• Recommended regimen: prednisolone 50 mg daily for 10 days OR prednisone 60 mg daily for 5 days followed by a 5-day taper 3
• Antiviral therapy alone is not recommended but may be offered in combination with oral steroids 2, 3
• Eye protection is essential for patients with impaired eye closure to prevent corneal damage 3

Prognosis

• Bell's palsy is typically self-limited, with most patients beginning to show recovery within 2-3 weeks 2
• Complete recovery typically occurs within 3-4 months for most patients 2
• Without treatment, facial function is completely restored in approximately 70% of patients with complete paralysis within 6 months, and up to 94% of patients with incomplete paralysis 2
• Approximately 30% of patients may experience permanent facial weakness with muscle contractures 3

Common Pitfalls in Diagnosis

• Failing to test forehead function can lead to misdiagnosis, as it is critical to distinguish Bell's palsy from central causes of facial weakness 3
• Mistaking other causes of facial paralysis (such as tumors, trauma, or infection) for Bell's palsy can delay appropriate treatment 4, 5
• Bilateral facial weakness is rare in Bell's palsy and suggests an alternative diagnosis 3
• Delayed presentation of facial paralysis after trauma should prompt investigation for temporal bone fracture 6