aetiology

Last reviewed 01/2018

• 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
  • severe hypertension
  • last trimester of pregnancy
  • dental anaesthesia
  • the common cold

Reference:

• (1) Holland NJ et al. Recent developments in Bell's palsy. BMJ  2004;329:553-557
• (2) Effrey D. Tiemstra, et al, Bell's Palsy: Diagnosis and Management, Am Fam Physician 2007;76:997-1002, 1004.
• (3) Gilden DH. Bell's Palsy. N Engl J Med September 23, 2004; 351:1323