What is the viral etiology of Bell's (Bell's) palsy?

From the Guidelines

Bell's palsy is primarily associated with herpes simplex virus type 1 (HSV-1) infection, though other viruses may also play a role. The condition occurs when viral reactivation leads to inflammation of the facial nerve within the narrow facial canal, causing compression and subsequent facial muscle weakness or paralysis. HSV-1 has been detected in the endoneurial fluid and posterior auricular muscle in affected patients, supporting its etiological role 1. Varicella-zoster virus (VZV) is another significant viral cause, particularly in cases diagnosed as Ramsay Hunt syndrome when accompanied by vesicles. Other implicated viruses include Epstein-Barr virus, cytomegalovirus, and adenovirus, though with less substantial evidence.

Key Points

• The viral etiology explains why antiviral medications like acyclovir or valacyclovir (typically 1000mg three times daily for 7 days) are often prescribed alongside corticosteroids (prednisolone 60-80mg daily for 5-7 days, tapered over 10-14 days) for treatment, especially when started within 72 hours of symptom onset 1.
• The virus is thought to cause inflammation and edema of the facial nerve, leading to compression within the bony facial canal and subsequent nerve damage and facial weakness.
• Antiviral therapy alone is no better than placebo with regard to facial nerve recovery in Bell’s palsy 1.
• The use of oral steroids in children is not well supported by quality trials, but may be considered in pediatric patients with a large role for caregiver involvement in the decision-making process 1.

Treatment Considerations

• Clinicians should prescribe oral steroids within 72 hours of symptom onset for Bell’s palsy patients 16 years and older 1.
• Clinicians may offer oral antiviral therapy in addition to oral steroids within 72 hours of symptom onset for patients with Bell’s palsy 1.
• Eye protection should be implemented for Bell’s palsy patients with impaired eye closure 1.

From the Research

Viral Etiology of Bell's Palsy

• The exact cause of Bell's palsy remains unclear, but several studies suggest a link between herpes simplex virus type 1 (HSV-1) and the condition 2, 3.
• A study published in 1997 found that HSV DNA was detectable in the geniculate ganglia of patients with Bell's palsy, providing evidence for the reactivation of HSV genomes as a potential cause of the condition 2.
• Another study published in 2010 discussed the controversy surrounding the use of antiviral agents in the treatment of Bell's palsy, with some studies suggesting that antivirals may be beneficial in treating patients with severe or complete facial paralysis 4.
• A multicenter, randomized, placebo-controlled study published in 2007 found that treatment with valacyclovir and prednisolone was more effective than treatment with prednisolone alone in patients with Bell's palsy, excluding zoster sine herpete 5.

Treatment Implications

• The use of antiviral agents, such as valacyclovir, in combination with corticosteroids, such as prednisolone, may be beneficial in treating patients with Bell's palsy, particularly those with severe or complete facial paralysis 4, 5.
• A study published in 2023 found that steroid monotherapy was effective in treating Bell's palsy, but combined treatment with antivirals may have potential advantages, especially in patients with more severe disease 6.
• The timing of treatment initiation is also an important factor, with earlier treatment initiation associated with better recovery rates 6.

Herpes Simplex Virus Type 1 (HSV-1) and Bell's Palsy

• Several studies have suggested a link between HSV-1 and Bell's palsy, with evidence of HSV-1 DNA detection in the geniculate ganglia of patients with the condition 2, 3.
• The reactivation of HSV-1 genomes from the geniculate ganglia is thought to be a potential cause of Bell's palsy, leading some to suggest that the condition be renamed "herpetic facial paralysis" 2.