8. Idiopathic facial nerve palsy, Bell palsy

Facial nerve palsy is a peripheral lesion of the facial nerve. In the cases where this lesion is idiopathic, the condition is called Bell’s palsy.

Etiology

• Idiopathic (= Bell’s palsy)
• Infection
  • VZV (herpes zoster oticus/Ramsay Hunt syndrome)
  • Lyme disease
• Trauma (involving pyramidal bone)
• Parotid tumour
• Brainstem stroke (involving facial nucleus)

Bell’s palsy is caused by idiopathic inflammation of CN VII in the facial canal. It might be due to viral infection, especially HSV.

Clinical features

Symptoms of peripheral facial palsy are ipsilateral to the lesion and affect both the lower and upper half of the face. Symptoms include:

• Motor symptoms
  • Frowning, eye-closing, blinking is impaired
  • Inability to close the eye
  • Drooping corner of mouth
  • Disappearance of nasolabial fold
• Pain behind the ear
• Hyperacusis
• Abnormal lacrimation
• Abnormal taste

If Lyme disease is the cause, the facial palsy may be bilateral.

Diagnosis and evaluation

To evaluate for the motor symptoms, ask the patient to grin with teeth, close their eyes, and wrinkle the forehead. The tympanic membrane and ear canal should be evaluated for herpes blister by otoscope. If peripheral facial palsy is the only symptom, Bell’s palsy is assumed, and no further investigation is needed. If other symptoms are present, investigate with MRI or LP to look for other causes.

Treatment

In most cases Bell’s palsy resolves completely in a few weeks without treatment. Corticosteroids hasten the resolution if given within the first 3 days of symptoms. Acyclovir can be used if viral etiology is suspected.

To prevent atrophy the patient should do physiotherapy of the face. To prevent keratitis if the patient can’t close the eye completely, artificial eye drops must be used to prevent dry eyes.