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Bell palsy accounts for 80% of cases of unilateral lower motor neuron facial paralysis1
It has an annual incidence of 20–30 cases per 100 000 population2 and can occur at any age; median age at onset is 40 years.2 The cause is unknown, although the herpes simplex viral genome is detected in the facial nerve endoneurial fluid in 79% of cases.1–3
Onset is sudden and paralysis progresses within hours, affecting muscles of facial expression, including those in the forehead
Complete paralysis includes impaired forehead wrinkling, ptosis, incomplete lid closure and a flattened nasolabial fold.4 Bell palsy is diagnosed clinically, and no tests are indicated unless the presentation is atypical.1 A neurologic examination should look for evidence of stroke, multiple sclerosis and brain cancers. Bilateral presentations should raise suspicion for a systemic disease such as sarcoidosis, Guillain–Barré syndrome or Lyme disease.
Without treatment, 70% of patients with complete and 94% with incomplete paralysis will recover facial function within 6 months4
The House–Brackman severity score can be used to assess recovery.4,5 Recurrence occurs in 7%–8% of patients.2,3 Older age, hypertension, loss of taste and complete paralysis are risk factors for a poorer prognosis.2 Persistent complications include abnormal facial muscle movement, tearing and lacrimation.1–4
Patients with Bell palsy should receive corticosteroids within 48 hours of symptom onset, regardless of severity
Treatment with a total of 450–500 mg prednisone over 10 days has a number needed to treat of 8 to achieve a House–Brackman score of grade 2 or less after 4 months for patients with severe or complete paralysis.5 Antiviral medications can be considered in severe cases.4,5 Eye protection (sunglasses, eye patch, lubricating tears or ointments) should be used routinely to prevent corneal abrasions, ulceration and keratitis.4,5 Other options for persistent symptoms include facial physiotherapy for weakness, botulinum toxin injections for facial asymmetry and surgery to facilitate eyelid closure.3,4
Investigation for upper motor neuron lesions or local compressive disorders should be considered for patients with new symptoms, progressive weakness or incomplete recovery4,5
New symptoms warrant investigation at any time; incomplete recovery should be investigated at 3 months or later. Clinicians should consider brain imaging (computed tomography or magnetic resonance imaging), electromyography and referral to a neurologist or otolaryngologist.
This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY-NC-ND 4.0) licence, which permits use, distribution and reproduction in any medium, provided that the original publication is properly cited, the use is noncommercial (i.e., research or educational use), and no modifications or adaptations are made. See: https://creativecommons.org/licenses/by-nc-nd/4.0/
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