Introduction

Bell's palsy is a weakness (or palsy) of muscles and loss of functions innervated (provide nerve input) by the Facial Nerve (Cranial nerve VII).  This weakness is likely the result of inflammatory swelling of the facial nerve. Patients with this condition generally present with acute facial paralysis.  Bell's palsy occurs in approximately 25 out of 100,000 people annually. The exact cause of Bell's palsy is not known, but in many cases a viral infection may be playing a role, including the herpes virus in particular.  Where Lyme disease is endemic, it needs to be considered and requires antibiotics if strongly suspected or confirmed.

Symptoms

One of the earliest signs of Bell's palsy is a sharp ache behind the ear on the affected side, often after a viral infection or towards the end of pregnancy or just after delivery. This is followed by weakness of mouth movement and eye closure resulting in a unilateral facial droop.  People also can experience change in subjective taste (loss of taste sensation on the anterior 2/3 of the tongue on that side), blurry vision (from cornea exposure and eye dryness from reduced tear production on that side due to lacrimal gland denervation), changes in hearing (hyperacusis where loud sounds are perceived as louder or painful from the ear on that side), and problems with slurring, drooling, and eating and sometimes tingling sensations on the affected half of the face. These symptoms may develop over the course of several hours or a day. The severity of the symptoms varies from person to person. Even mild cases of Bell's palsy may take many months to resolve. As a general rule, the more severe the facial weakness, the longer the recovery will be.

Diagnosis

There is no single test to diagnose Bell's palsy. Other conditions such as injury, stroke and tumor will need to be ruled out clinically and sometimes in atypical cases with an imaging study such as magnetic resonance imaging (MRI) or computerized tomography (CAT) scan.  Blood work to look for conditions such as Lyme's disease, B12 deficiency and inflammatory states that may result in weakness of the facial nerve may also be ordered.  Risk is increased in people with diabetes.

Treatment

People with idiopathic (no known cause) Bell's palsy are usually treated with a short course of steroids (such as prednisone) to decrease swelling of the nerve. An antiviral medication, such as acyclovir, may also be prescribed for possible viral etiologies.  Cornea protection is important if eye blinking and tear production are limited.  Prognosis is generally good with significant recovery seen in the first 3 months, but residual weakness still present at that point can improve slowly over a year or more. Physical therapy offers limited benefit in some cases and may be recommended. Infrequent late complications may include spontaneous abnormal muscle spasm or involuntary movements on the formerly paralyzed side or abnormal tearing from that eye. Botox may have a treatment role for some of those late complications.