Definition and Overview
Bell's palsy refers to idiopathic facial nerve palsy -- an acute inflammatory condition and edema of the seventh cranial nerve (facial nerve) that causes sudden onset of unilateral facial motor paralysis.
The annual incidence is approximately 15 to 30 per 100,000 population, making it the most common cause of unilateral facial paralysis [1]. It can occur at any age but is most frequent between ages 15 and 45, with increased risk in pregnant women and patients with diabetes.
Etiology and Pathophysiology
Reactivation of latent herpes simplex virus type 1 (HSV-1) within the nerve ganglion is considered the most likely cause [2]. The reactivated virus travels along the facial nerve, inducing intraneural inflammation and edema, and the nerve becomes compressed within the narrow facial canal, resulting in paralysis.
Other causes include Ramsay Hunt syndrome due to varicella-zoster virus (VZV), Lyme disease, and otitis media, which constitute secondary facial paralysis and should be distinguished from Bell's palsy.
Symptoms
The typical presentation is complete loss of motor function on one side of the face, with the following findings:
- Loss of forehead wrinkles and inability to raise the brow
- Inability to fully close the eye (lagophthalmos), with tearing
- Drooping of the corner of the mouth, drooling of food
- Postauricular pain: often preceding paralysis onset by 1 to 2 days
- Taste impairment (anterior two-thirds of tongue)
- Hyperacusis: when the stapedius muscle is paralyzed
Symptoms progress over hours to days, with most patients reaching maximum paralysis within 72 hours.
Diagnosis
Bell's palsy is a clinical diagnosis. The key steps are confirming peripheral facial paralysis affecting the entire face including the forehead, and excluding secondary causes.
Differentiation from central facial paralysis (stroke, brain tumor) is critical. In central lesions, the upper motor neuron of the corticospinal tract is damaged, and because the forehead receives partial bilateral cortical innervation, forehead wrinkles are relatively preserved. Involvement of the forehead suggests a peripheral lesion.
- Blood tests: glucose, thyroid function, CBC to exclude secondary causes
- MRI: performed when atypical features are present (bilateral, progressive worsening, recurrence) to exclude tumors
- Nerve conduction study (NCS) / electromyography (EMG): used to assess the degree of nerve damage and predict prognosis
Treatment
Early treatment within 72 hours of onset is critical for prognosis.
Corticosteroids are the first-line treatment. Prednisolone 1 mg/kg/day (maximum 60-80 mg/day) for 5 to 7 days followed by a taper is recommended. The number needed to treat (NNT) has been reported as approximately 10.7 [3].
Antiviral agents may be considered in combination with corticosteroids for severe Bell's palsy. Acyclovir or valacyclovir are used, though antiviral monotherapy is inferior to corticosteroids [4].
Eye protection is essential when eye closure is impaired. Artificial tears, ophthalmic ointment, nighttime eye patches, and protective eyewear prevent corneal damage.
Physical therapy (facial muscle exercise rehabilitation) may help prevent synkinesis and promote functional recovery during the recovery phase.
Prognosis
Complete recovery occurs in approximately 70% of patients, with most reaching maximum recovery within 3 to 6 months of onset [1]. Patients with incomplete paralysis have a better prognosis than those with complete paralysis.
Approximately 15% may have mild sequelae (synkinesis, crocodile tears syndrome), and about 5% experience persistent severe sequelae. The recurrence rate is approximately 7 to 10%, and recurrence warrants further evaluation for secondary causes.
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This information is provided for medical educational purposes only and does not replace professional medical advice.
If you are experiencing symptoms, please consult a specialist.
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