In most cases the cause is unknown and is supposed to be associated with the inflammation of the facial nerve, which is believed to injure the nerve by applying pressure on it within the bone canal that the nerve passes through. In the remaining cases, a wide variety of pathological conditions may result in facial palsy including tumor, meningitis, stroke, diabetes mellitus, head trauma and inflammatory diseases of the cranial nerves (sarcoidosis, brucellosis etc). However, in these conditions, the neurologic findings are rarely restricted to the facial nerve and usually involve the neighbouring structures, as well. One interesting disease difficult to exclude in the differential diagnosis is herpes zoster virus infection of the facial nerve. Although the major difference of this disease is vesicular skin changes in the external ear canal, this finding may occasionally be lacking.
A patient with facial palsy is expected to present with sole motor symptoms. Detection of sensory loss, hearing loss or ataxia during medical examination excludes the diagnosis of Bell's palsy and requires further examination for diagnosis.
The treatment is a matter of controversy. In a case presenting with incomplete facial palsy, the treatment is usually unnecessary. However, patients presenting with complete paralysis (unable to close one side of his/her eyes and corner of mouth) are usually treated with corticosteroids, efficacy of which has never been tested reliably. Most of the patients (60-80%) recover completely within few weeks (sometimes within 3 months) and the rest may recover with permanent deficits in varying degrees. Surgical procedures to decompress the facial nerve have not been proven reliably beneficial.
Major expected complications are chronic loss of taste, chronic facial spasm and corneal infections. Therefore, the eyes should be protected by covers, and eye drops or eye ointments may be recommended especially for cases with complete paralysis.