[Cause of Bell's palsy: herpes simplex virus].

At present Bell's palsy (BP) is still defined as idiopathic unilateral facial paralysis of sudden onset. More than 20 years ago an aetiological link between herpes simplex virus (HSV) and BP was proposed. Numerous experiments in animals and in humans have been performed to test this hypothesis. However, the human facial nerve tissue itself was investigated in only a few of these studies. Two research lines were followed: (a) search for presence of latent HSV in the facial nerve of asymptomatic individuals (as shown earlier in the trigeminal nerve); (b) find 'active' HSV in tissues from BP patients with recent onset of disease. The application of new molecular biological techniques, notably polymerase chain reaction (PCR), to facial nerve tissues has provided ample evidence for a causal relationship between BP and HSV. Therefore it might now be the time to change the name 'Bell's palsy' into 'herpetic facial paralysis'.