Bell's palsy

Bell's palsy is an acute peripheral facial palsy — sudden weakness or total paralysis of the muscles on one side of the face caused by inflammation and swelling of the seventh cranial nerve (facial nerve). As the swollen nerve presses against the narrow bony canal through which it passes, nerve conduction is impaired and facial muscle control is lost.

The exact cause is unknown but is believed to involve a viral trigger — most commonly reactivation of herpes simplex or herpes zoster virus. Other viruses linked to Bell's palsy include Epstein-Barr, cytomegalovirus, adenovirus, rubella, mumps, influenza B, and coxsackievirus. Bell's palsy can occur at any age.

**Symptoms** appear suddenly and include: - Rapid onset of mild weakness to complete paralysis on one side of the face — within hours to days - Facial drooping; inability to close the eye or smile on the affected side - Drooling - Pain around the jaw or behind the ear on the affected side - Increased sound sensitivity (hyperacusis) on the affected side - Headache - Loss of taste - Changes in tear and saliva production - Rarely, both sides of the face are affected

**Prognosis:** Most cases are temporary. Symptoms begin to improve within a few weeks, with complete recovery in about 6 months. A small minority have permanent symptoms. Bell's palsy can rarely recur.

**Complications** in severe cases include: - Permanent damage to the facial nerve - Synkinesis — abnormal nerve fibre regrowth causing involuntary muscle contractions (e.g., the eye closes when smiling) - Corneal damage from inability to close the eye (exposure keratopathy)

**Medical treatment:** Corticosteroids (prednisone) started within several days of symptom onset reduce nerve inflammation and improve recovery rates. Antiviral drugs (valacyclovir, acyclovir) may be added in severe cases, though evidence remains mixed. Eye protection is essential when the eye cannot close.