It is the most common form of facial paralysis. It is an idiopathic palsy of the Vllth (facial) nerve resulting in a usually unilateral facial weakness or paralysis of lower motor neuron type. The annual incidence of this idiopathic disorder is 25:100,000 annually or about 1 in 60 persons in a lifetime.
Bell's palsy has been associated with the presence of herpes simplex virus (HSV) type 1 DNA in endoneurial fluid and posterior auricular muscle, suggesting that a reactivation of this virus in the geniculate ganglion may be responsible. It is believed that viral infection causes the nerve to swell and get entrapped in the facial nerve canal. Diabetes and hypertension are important predisposing factors.
The onset of Bell's palsy is fairly abrupt and rapid, with maximal weakness being attained by 48 hrs and associated with pain behind the ear which may precede the paralysis for a day or two. Weakness worsens for 1-2 days before stabilizing and pain resolves within a few days.