From the Guidelines
The exact cause of Bell's palsy is not fully understood, but it's believed to result from inflammation and swelling of the facial nerve (cranial nerve VII), most commonly triggered by viral infections, particularly herpes simplex virus (HSV-1) and herpes zoster virus. This inflammation causes compression of the facial nerve as it passes through the narrow bony canal in the skull, leading to damage or dysfunction of the nerve, resulting in weakness or paralysis of the facial muscles on the affected side 1. The condition is characterized by acute unilateral facial nerve paresis or paralysis with onset in less than 72 hours and without identifiable cause, and it is often associated with symptoms such as dryness of the eye or mouth, taste disturbance or loss, hyperacusis, and sagging of the eyelid or corner of the mouth.
Key Points
- The inflammation of the facial nerve is thought to be caused by viral infections, including herpes simplex virus (HSV-1), herpes zoster virus, Epstein-Barr virus, cytomegalovirus, and adenovirus 1.
- Risk factors for Bell's palsy include pregnancy, diabetes, upper respiratory infections, and compromised immune systems.
- Bell's palsy typically develops suddenly, reaching maximum severity within 72 hours, and most patients (about 70-85%) recover completely within 3-6 months, even without treatment 1.
- Treatment often includes corticosteroids like prednisone (typically 60-80mg daily for 7-10 days) to reduce inflammation, sometimes combined with antiviral medications like acyclovir or valacyclovir if started within 72 hours of symptom onset 1.
Diagnosis and Treatment
- Clinicians should 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 prescribe oral steroids within 72 hours of symptom onset for Bell’s palsy patients 16 years and older, and may offer oral antiviral therapy in addition to oral steroids within 72 hours of symptom onset for patients with Bell’s palsy 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
Cause of Bell's Palsy
The exact cause of Bell's palsy is unknown, but several factors are thought to contribute to its development, including:
- Immune pathways 2
- Viral pathways, with some evidence suggesting a viral etiology 3, 4
- Ischemic pathways, with possible ischaemic compression of the seventh cranial nerve 2
- Inflammation and oedema of the facial nerve 5
Risk Factors
Certain groups of people are more likely to develop Bell's palsy, including:
- Pregnant women 2, 6
- People with diabetes 2, 6
- People with respiratory infections 2
- People with a family history of Bell's palsy, suggesting a possible hereditary component 2
Pathophysiology
Bell's palsy is characterized by the spontaneous acute onset of unilateral peripheral facial paresis or palsy in isolation, with no features from the history, neurologic examination, or head and neck examination suggesting a specific or alternative cause 3. The condition is thought to result from damage to the seventh cranial nerve, which can be caused by a variety of factors, including viral inflammation and ischaemic compression 2.