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 type 1 (HSV-1) 1.
Definition and Diagnosis
Bell's palsy is defined as acute unilateral facial nerve paresis or paralysis with onset in less than 72 hours and without an identifiable cause 1. The diagnosis of Bell's palsy requires the careful elimination of other causes of facial paresis or paralysis, and it is a diagnosis of exclusion 1.
Pathophysiology
The inflammation leads to compression of the facial nerve as it passes through the narrow bony canal in the skull, resulting in damage to the protective covering of the nerve 1. This damage disrupts the transmission of nerve signals to the facial muscles, causing weakness or paralysis on one side of the face.
Risk Factors
Risk factors for Bell's palsy include pregnancy, diabetes, upper respiratory infections, and compromised immune systems 1.
Prognosis
Most cases of Bell's palsy are temporary, with symptoms typically improving within a few weeks and complete recovery within six months, though some people may experience permanent facial weakness 1.
Some key points to consider in the management of Bell's palsy include:
- 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 1.
- Clinicians should implement eye protection for Bell’s palsy patients with impaired eye closure 1.
Overall, while the exact cause of Bell's palsy is not fully understood, it is believed to result from inflammation and swelling of the facial nerve, most commonly triggered by viral infections. Prompt diagnosis and treatment can help improve outcomes and reduce the risk of complications.
From the Research
Cause of Bell's Palsy
The cause of Bell's palsy is not fully understood, but several factors have been suggested as possible contributors:
- Viral infection or reactivation of latent viruses, such as herpes simplex and herpes zoster, which may provoke an autoimmune reaction against peripheral nerve myelin components 2, 3, 4, 5
- Autoimmune disease, with a cell-mediated autoimmune mechanism against a myelin basic protein suggested for the pathogenesis of Bell's palsy 2
- Inflammation of the facial nerve at the geniculate ganglion, which may be caused by various factors, including viral infections and autoimmune disorders 3
- Bacterial infection, which may be related to some cases of Bell's palsy, although this is not widely accepted as a primary cause 6
Possible Pathomechanisms
The pathogenesis of Bell's palsy is believed to involve:
- Demyelination of cranial nerves, especially the facial nerve, due to an autoimmune reaction or viral infection 2, 5
- Inflammation and entrapment of the nerve in the bony foramen, which can lead to nerve degeneration and paralysis 2, 4
- Reactivation of latent herpes viruses from cranial nerve ganglia, which may trigger an autoimmune response and lead to Bell's palsy 2, 4