Bell's palsy is a facial paralysis, usually unilateral, and of sudden onset.
It is a lower motor neurone palsy usually diagnosed by exclusion. Typically, presentation is with facial distortion, loss of taste, hyperacusis and a watery eye.
palsy was previously considered as an idiopthic lower motor neurone nerve paly
but there has been increasing evidence to suggest that the main cause of Bell's
palsy is latent herpes viruses (herpes simplex virus type 1 and herpes zoster
virus), which are reactivated from cranial nerve ganglia
- polymerase chain reaction techniques have isolated herpes virus DNA from the facial nerve during acute palsy
- inflammation of the nerve initially results in a reversible neurapraxia - however ultimately Wallerian degeneration ensues
- herpes zoster virus appears to exhibit more aggressive biological behaviour than herpes simplex virus type 1 - this is because it spreads transversely through the nerve by way of satellite cells
Note that a fifth of cases of acute facial palsy have an alternative cause that should be managed appropriately.