From the Guidelines
Bell's palsy is primarily caused by inflammation and swelling of the facial nerve, with a suspected viral etiology, although the exact mechanism is currently unknown. The condition is characterized by acute unilateral facial nerve paresis or paralysis with onset in less than 72 hours and without identifiable cause 1. According to the clinical practice guideline, the facial nerve inflammation and edema are thought to result from a viral infection, which may lead to nerve compression and temporary or permanent nerve damage 1.
Key Points
- The exact cause of Bell's palsy is often unknown, but viral infections are believed to be the most common trigger 1
- Herpes simplex virus type 1 and herpes zoster virus are frequently implicated, although other potential causes include bacterial infections, Lyme disease, diabetes, high blood pressure, and autoimmune disorders
- The inflammation causes the nerve to become compressed within the narrow bony canal through which it travels, leading to damage and disruption of nerve signals to facial muscles 1
- Environmental factors like cold exposure may trigger Bell's palsy in susceptible individuals
Clinical Presentation
Patients with Bell's palsy may experience dryness of the eye or mouth, taste disturbance or loss, hyperacusis, and sagging of the eyelid or corner of the mouth, as well as ipsilateral pain around the ear or face 1. The incidence of Bell's palsy is highest in the 15- to 45-year-old age group, and most patients show some recovery without intervention within 2 to 3 weeks after onset of symptoms 1.
Treatment and Prognosis
Most cases of Bell's palsy resolve spontaneously within 3-6 months, though treatment with corticosteroids like prednisone started within 72 hours of symptom onset can improve recovery rates 1. Antiviral medications may be added if a herpes virus is suspected, although the benefit of surgical decompression of the facial nerve remains relatively controversial 1.
From the Research
Causes of Bell's Palsy
The exact cause of Bell's palsy is unknown, but several factors are thought to contribute to its development, including:
- Ischaemic compression of the seventh cranial nerve, which could be caused by viral inflammation 2
- Immune, viral, and ischemic pathways are all thought to play a role in the development of Bell paralysis 2
- Infection with herpes simplex virus type 1 is a possible etiology 3
- Reactivation of herpes viruses from the geniculate ganglion of the facial nerve may cause a proportion of cases 4
- Trauma or inflammation of the 7th cranial nerve or facial nerve or its branches along its course, primarily in the bony canal 5
Risk Factors
Certain groups of people are at a higher risk of developing Bell's palsy, including:
- Diabetics 5, 3
- Hypertensives 5
- Pregnant women 5, 2
- Obese individuals 5
- People with upper respiratory tract infections 5
- People with a history of Bell's palsy or a family history of the condition 2
Pathophysiology
Bell's palsy results from facial nerve dysfunction due to trauma or inflammation of the 7th cranial nerve or facial nerve or its branches along its course, primarily in the bony canal 5