The aetiology of Bell's palsy was previously stated as unknown.
However there is 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 (1,2).
herpes simplex virus type 1 ( HSV-1) is probably the cause of most cases of Bell's palsy (3)
research has found elevated HSV-1 titers in affected individuals (2)
it is thought to be due to virus reactivation from latency in the geniculate ganglion rather than primary infection (3)
herpes zoster virus has traditionally been associated with Ramsay Hunt syndrome (typical cutaneous vesicles and cochleovestibular dysfunction)
however vesiculation may not necessarily appear (zoster sine herpete) or may be delayed in up to half of patients
preherpetic neuralgia (dermatomal pain and dysaesthesia before vesiculation) may be the only clinical indicator that herpes zoster virus is involved
almost a third of facial palsies previously diagnosed as idiopathic are thought to be due to zoster sine herpete
In most patients, the condition occurs in isolation. Less commonly, it may be associated with:
diabetes mellitus
a viral polyneuropathy with inflammatory demyelination
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