A large percentage of cases of Bell's palsy may be caused by herpes-simplex virus (H.S.V.). It is suggested that H.S.V. takes up residence within the peripheral-nerve-cell axon, where it is protected from neutralising antibody and sensitised mononuclear immunocytes. Bell's palsy may result when H.S.V. ruptures from the nerve axon, infects the Schwann sheath, and progresses centripetally. When the swelling caused by the herpetic endoneuritis reaches the enclosed space of the bony fallopian canal, compression of the facial nerve results in paralysis.
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