What are the causes of Bell's (Bell's) palsy?

From the Guidelines

Bell's palsy causes facial weakness or paralysis on one side of the face due to inflammation or compression of the facial nerve (cranial nerve VII). This condition typically develops suddenly, often overnight, and results in drooping of the affected side of the face, difficulty closing the eye, decreased tear production, drooling, loss of taste on the anterior two-thirds of the tongue, and hypersensitivity to sound 1. The exact cause is unknown, but viral infections, immune disorders, or local ischemia are believed to trigger inflammation of the nerve within the facial canal.

Key Symptoms and Effects

• Dryness of the eye or mouth
• Taste disturbance or loss
• Hyperacusis
• Sagging of the eyelid or corner of the mouth
• Ipsilateral pain around the ear or face Most cases (about 70-85%) resolve spontaneously within 3-6 months, but treatment with oral corticosteroids started within 72 hours of symptom onset improves outcomes 1.

Treatment Recommendations

• Oral steroids should be prescribed within 72 hours of symptom onset for Bell’s palsy patients 16 years and older 1
• Antiviral medications like acyclovir or valacyclovir may be added in severe cases
• Eye protection with artificial tears during the day and lubricating ointment at night is crucial to prevent corneal damage when eye closure is impaired 1
• Physical therapy with facial exercises may help maintain muscle tone during recovery, although the evidence for this is not strong 1. It is essential to assess the patient using history and physical examination to exclude identifiable causes of facial paresis or paralysis in patients presenting with acute-onset unilateral facial paresis or paralysis 1. Clinicians should implement eye protection for Bell’s palsy patients with impaired eye closure and reassess or refer to a facial nerve specialist those Bell’s palsy patients with new or worsening neurologic findings at any point, ocular symptoms developing at any point, or incomplete facial recovery 3 months after initial symptom onset 1.

From the Research

Causes of Bell's Palsy

• Inflammation and oedema of the facial nerve are implicated in causing Bell's palsy 2, 3, 4

Treatment of Bell's Palsy

• Corticosteroids have a potent anti-inflammatory action which should minimise nerve damage and thereby improve the outcome of patients suffering from this condition 2, 3, 4
• The available evidence from randomised controlled trials shows significant benefit from treating Bell's palsy with corticosteroids 3, 4
• Antiviral treatment may have little or no effect on rates of incomplete recovery in people with Bell's palsy compared to corticosteroids alone 5
• The combination of antivirals and corticosteroids may reduce the late sequelae of Bell's palsy compared with corticosteroids alone 5

Recovery Rates

• Recovery rates were better in participants receiving corticosteroids alone than antivirals alone 5
• The rate of incomplete recovery was lower with antivirals plus corticosteroids than with placebo or no treatment 5
• Antivirals alone had no clear effect on incomplete recovery rates compared with placebo 5

Adverse Events

• There was no clear difference in adverse events from the use of antivirals compared with either placebo or corticosteroids 5
• The evidence is too uncertain to draw conclusions about adverse events 5