From the Guidelines
Bell's palsy is caused by inflammation and swelling of the facial nerve, with viral infections, particularly herpes simplex virus (HSV-1) and herpes zoster virus, being the most common suspected cause. The exact trigger is often unknown, but other potential causes include bacterial infections, Lyme disease, diabetes, high blood pressure, and autoimmune disorders 1. The inflammation causes the nerve to become compressed within the narrow bony canal it passes through in the skull, leading to damage and disruption of nerve signals to facial muscles. This results in weakness or paralysis on the affected side of the face, causing symptoms like drooping of the mouth, inability to close the eye, decreased tear production, and difficulty with facial expressions.
Key Points
- The facial nerve carries nerve impulses to muscles of the face and also to the lacrimal glands, salivary glands, stapedius muscle, taste fibers from the anterior tongue, and general sensory fibers from the tympanic membrane and posterior ear canal 1.
- Most cases of Bell's palsy are temporary, with recovery typically occurring within 3-6 months as inflammation subsides and nerve function returns.
- Treatment often includes corticosteroids like prednisone to reduce inflammation, sometimes combined with antiviral medications like acyclovir if a viral cause is suspected 1.
- Eye protection is essential during recovery to prevent corneal damage, and clinicians should implement eye protection for Bell’s palsy patients with impaired eye closure 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 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.
From the Research
Causes of Bell's Palsy
- The exact cause of Bell's palsy is unknown 2, 3, 4, but it is thought to result 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 2.
- Immune, viral, and ischemic pathways are all thought to play a role in the development of Bell paralysis 3.
- Infection with herpes simplex virus (HSV) type 1 may be a major cause of Bell's palsy 5.
- Varicella zoster virus (VZV) reactivation (Ramsay Hunt syndrome) is less common, but may appear without skin lesions in a form indistinguishable from Bell's palsy 5.
- Risk factors for Bell's palsy include diabetes, hypertension, pregnancy, obesity, and upper respiratory tract infections 2, 3, 4.
Possible Triggers
- Recent viral infection, especially herpes simplex 4.
- Ischaemic compression of the seventh cranial nerve, which could be caused by viral inflammation 3.
- Edema, entrapment, or inflammation of the seventh cranial nerve 4.
Research Findings
- Studies have shown that antiviral agents such as acyclovir may be effective in treating Bell's palsy, especially when used with oral steroids 5, 6.
- Administration of acyclovir before and after facial nerve paralysis has been shown to reduce the incidence and duration of facial nerve paralysis in animal models 6.