Idiopathic facial nerve (Bell) palsy
Idiopathic facial nerve (Bell) palsy is the most common cranial neuropathy. The cause is uncertain, but the palsy might be related to a virus infection. Consider the differential diagnosis of facial nerve palsy, as many other conditions (eg diabetes, hypertension, parotid tumours, tick bites, trauma) can affect the facial nerve—the treatment is different from that for idiopathic facial nerve (Bell) palsy. If vesicles are seen in the ipsilateral ear, varicella zoster virus infection of the facial nerve (Ramsay-Hunt syndrome) is the probable cause—treat with prednisolone (or prednisone) as below, plus an antiviral drug. If the palsy has atypical features (eg bilateral involvement) or recovery is prolonged, refer for magnetic resonance imaging and expert review to exclude other diagnoses.
Many patients with idiopathic facial nerve (Bell) palsy return to normal with no residual weakness. If a lower motor neurone facial palsy is mild and incomplete, the outlook for recovery is so good that treatment may not be needed. If the paralysis is complete or nearly complete, or the sense of taste is lost on the anterior two-thirds of the tongue on the affected side, the prognosis for complete recovery is still good but less certain. Advise patients that facial nerve recovery can take several weeks or months. Depending on the severity of facial nerve involvement, some weakness may persist.
When the patient has had symptoms of idiopathic facial nerve (Bell) palsy for less than 72 hours, evidence supports starting treatment with a corticosteroid1. Use:
prednisolone (or prednisone) 1 mg/kg (up to 75 mg) orally, once daily in the morning for 5 days. idiopathic facial nerve (Bell) palsy prednis ol one
A 2015 systematic review concluded that low-quality evidence showed a benefit from combining a corticosteroid with an antiviral drug, compared with the corticosteroid alone2.
If eye closure is impaired, cover the eye on the affected side in windy or dusty surroundings and instil artificial tears liberally. Ophthalmological review is often helpful if the facial nerve palsy is severe.
After recovery from facial nerve palsy, aberrant regeneration of the facial nerve can have adverse effects (eg co-contraction of facial muscles [synkinesis], involuntary tearing of the eye on the affected side when eating [crocodile tears], gustatory sweating).