Bell’s palsy is an idiopathic peripheral (lower motor neurone) facial weakness (prosopoplegia). It is thought to result from viral inflammation of the facial (VII) nerve. Other causes of lower motor neurone facial paresis (q.v.) may need to be excluded before a diagnosis of Bell’s palsy can be made.
In the majority of patients with Bell’s palsy (idiopathic facial paresis), spontaneous recovery occurs over three weeks to two months. Poorer prognosis is associated with older age (over 40 years) and if no recovery is seen within four weeks of onset. The efficacy of steroid treatment remains uncertain, but it is often prescribed; it may improve facial functional outcome.
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Williamson IG, Whelan TR. The clinical problem of Bell’s palsy: is treatment with steroids effective? British Journal of General Practice1996; 46: 743-747