Facial Nerve Palsy

Facial nerve palsy refers to weakness of the facial muscles on one side of the face (a partial loss of movement), whereas paralysis means a complete absence of movement. This condition develops when the facial nerve (cranial nerve VII) is damaged or its function is impaired.

The most common form is idiopathic facial paralysis, known as Bell’s palsy. It develops suddenly, usually without an identifiable cause. This type of paralysis is peripheral, meaning that the nerve itself is affected after exiting the brainstem.

Aetiology and pathophysiology

The causes of facial nerve palsy are usually classified as primary (idiopathic) or secondary.

• Bell’s palsy. It is thought to result from viral reactivation, most often herpes simplex virus. The infection leads to swelling and inflammation of the nerve. As a result, the nerve to become compressed within the narrow bony canal of the temporal bone.
• Secondary palsies. These may be caused by infections (such as Lyme disease or herpes zoster), tumors, otitis media, trauma (including skull base fractures), stroke, or systemic diseases.

Clinical Significance

Symptoms typically appear suddenly and progress within a few hours. Facial asymmetry soon becomes evident: the nasolabial fold flattens, the corner of the mouth droops, and the patient is unable to wrinkle the forehead, raise the eyebrow, fully close the eye (lagophthalmos), or puff out the cheek. In addition, taste disturbances and increased sensitivity to sound (hyperacusis) may occur.

Diagnosis is primarily based on clinical examination. Particular attention should be given to excluding secondary causes, especially stroke. Treatment of Bell’s palsy is most effective when started within the first 72 hours and usually includes corticosteroids to reduce nerve swelling. Eye protection and lubrication are essential to prevent corneal damage.

Differential Diagnosis

It is important to distinguish between peripheral facial palsy, such as Bell’s palsy, and central facial palsy, which may result from stroke. In peripheral palsy, the entire side of the face, including the forehead muscles, is affected. By contrast, central palsy partially preserves forehead movement because of bilateral cortical innervation, allowing the patient to still wrinkle the forehead.