Facial nerve palsy refers to isolated dysfunction of the facial nerve. This typically presents with a unilateral facial weakness. It is important to understand some basics about the pathway and function of the facial nerve.
Facial Nerve Pathway
The facial nerve exits the brainstem at the cerebellopontine angle. On its journey to the face, it passes through the temporal bone and parotid gland.
It then divides into five branches that supply different areas of the face:
- Marginal mandibular
Facial Nerve Function
There are three functions of the facial nerve: motor, sensory and parasympathetic.
It supplies the muscles of facial expression, the stapedius in the inner ear and the posterior digastric, stylohyoid and platysma muscles in the neck.
It carries taste from the anterior 2/3 of the tongue.
It provides the parasympathetic supply to the:
- Submandibular and sublingual salivary glands
- Lacrimal gland (stimulating tear production)
Upper Versus Lower Motor Neurone Lesion
A common exam task is to distinguish between an upper motor neurone and lower motor neurone facial nerve palsy. It is essential to make this distinction because, in a patient with a new-onset upper motor neurone facial nerve palsy, you should be referring immediately with a suspected stroke. In contrast, patients with a lower motor neurone facial nerve palsy can be managed with less urgency.
Each side of the forehead has upper motor neurone innervation by both sides of the brain. However, each side of the forehead only has lower motor neurone innervation from one side of the brain.
In an upper motor neurone lesion, the forehead will be spared, and the patient can move their forehead on the affected side.
In a lower motor neurone lesion, the forehead will NOT be spared, and the patient cannot move their forehead on the affected side.
You can differentiate between an upper and lower motor neurone lesion by asking the patient to raise their eyebrows. If they can raise both eyebrows and wrinkle both sides of the forehead, the patient has an upper motor neurone lesion. If the eyebrow on the affected side cannot be raised and the forehead remains smooth, the patient has a lower motor neurone lesion.
Upper Motor Neurone Lesions
Unilateral upper motor neurone lesions occur in:
- Cerebrovascular accidents (strokes)
Bilateral upper motor neurone lesions are rare. They may occur in:
- Pseudobulbar palsies
- Motor neurone disease
Bell’s palsy is a relatively common condition. It is idiopathic, meaning there is no apparent cause. It presents as a unilateral lower motor neurone facial nerve palsy. The majority of patients fully recover over several weeks, but recovery may take up to 12 months. A third are left with some residual weakness.
If patients present within 72 hours of developing symptoms, NICE clinical knowledge summaries (updated 2019) recommend considering prednisolone as treatment, either:
- 50mg for 10 days
- 60mg for 5 days followed by a 5-day reducing regime of 10mg a day
Patients also require lubricating eye drops to prevent the eye on the affected side from drying out and being damaged. If they develop pain in the eye, they need an ophthalmology review for exposure keratopathy. The eye can be taped closed at night.
Ramsay-Hunt syndrome is caused by the herpes zoster virus. It presents as a unilateral lower motor neurone facial nerve palsy. Patients stereotypically have a painful and tender vesicular rash in the ear canal, pinna and around the ear on the affected side. This rash can extend to the anterior two-thirds of the tongue and hard palate.
Treatment should ideally be initiated within 72 hours. Treatment is with:
Patients also require lubricating eye drops.
TOM TIP: Ramsay-Hunt syndrome is a very popular presentation in your MCQ exams. Look out for that patient with a facial nerve palsy and vesicular rash around their ear.
Other Causes of Lower Motor Neurone Facial Nerve Palsy
- Otitis media
- Malignant otitis externa
- Lyme’s disease
- Multiple sclerosis
- Guillain–Barré syndrome
- Acoustic neuroma
- Parotid tumours
- Direct nerve trauma
- Damage during surgery
- Base of skull fractures
Last updated July 2021