Bellís Palsy (BP) is the most common cause of facial paralysis worldwide. Its incidence is about 20 cases per 100,000 persons. Although not age-specific, it affects young and middle-aged adults most often. There is no bias towards either sex.
Right- and left-side facial palsy occurs equally. Climate is not a contributing factor. BP does, however, have a higher prevalence among lower socioeconomic groups. 70% of patients with BP relate a previous upper respiratory infection, and 10% have a family incidence of the disorder. During pregnancy or pregnancy-induced hypertension, the significant increase in vascular volume, particularly in the last trimester, triples the risk of facial neuropathy due to edema of the facial nerve and the resulting compression.
BP is a diagnosis of exclusion. Its cause remains unknown but reactivated herpes simplex virus (HSV) heads the list as the most probable cause. An acute inflammatory response results in swelling of the facial nerve within the myelin sheath, causes reduced circulation in the nerve. The disorder usually progresses for 7 to 10 days, with sudden onset of facial weakness. Recovery from BP begins at 3 weeks for most (85%) patients, with a full recovery by 6 months. Between 4 and 6% experience severe deformity with very little return to normal facial movement, and 10 to 15% will be bothered by asymmetrical movement of the facial muscles. Recurrence may be on the same or opposite side.
Nerve conduction does not become altered until about 3 days after degeneration has occurred. These changes are then detected by observing a widened palpebral fissure (the space between the margins of the eyelids), reduced nasolabial fold (smile line), and drooping corner of the mouth. A dry eye may result from reduced blinking. Pain behind the ear is a common symptom, along with fever, tinnitus, and a mild hearing deficit. A tumor should be suspected when there is (1) associated tics or spasms, (2) slow onset of paralysis, and (3) paralysis of isolated branches of the facial nerve.
The first priority in treating Bell's palsy or any type of facial paralysis is to eliminate the source of damage to the nerve as quickly as possible. Minor compression for a short time period can result in mild and temporary damage. As time goes on with constant or increasing compression, damage to the nerve can also increase.