Etiology
Bell's palsy (idiopathic)
- Thought to encompass about 50% of all cases of facial nerve palsy
- Idiopathic facial paralysis, but believed to be associated with herpes simplex virus.
- Rapid onset < 72 hours
- More common in 15–45‑year‑olds
- More common in those with diabetes, upper respiratory ailments, immunocompromised, and pregnant patients.
- Often accompanied by a viral prodrome.
- 70%–80% recover spontaneously, though complete resolution can take months.
- Permanently altered facial function can occur in about 15%, and about7% can experience recurrence of Bell's palsy.
- Rarely bilateral
- Treatment consists of antiviral and corticosteroid therapy, though the significance of these regimens remains unclear.
Infection
- Bacterial infections including otitis media, otitis externa, and mastoiditis can involve the facial nerve.
- Lyme disease, caused by the transmission of Borrelia burgdorferi via tick bites, causes 10% of facial nerve palsy cases.
- 25% of Lyme cases are bilateral.
- Herpes zoster virus can cause facial nerve palsy in addition to a classic painful vesicular eruption and is called Ramsay Hunt syndrome or genicular ganglionitis.
- These patients often have considerable pain and are less responsive to therapy.
- Other inciting infections include
- Diphtheria
- Enterovirus
- HIV
- Varicella
- Polio
- Mumps
- Leprosy
- Dengue fever
- Cat-scratch disease
Trauma
- Blunt or penetrating trauma
- Temporal bone fracture
- Facial nerve injury
- Iatrogenic
- Surgery of the face, neck, ear, and especially parotid gland
- Resection of cerebellopontine angle tumors can cause Horner's syndrome with cranial nerves V, VI, VII, and VIII palsy.
Neoplastic
- Central/nuclear lesions
- Tumors that can damage the facial nerve and usually present with a more gradual onset of paralysis compared with Bell's palsy or infection
- Brainstem/pons
- Cerebellopontine angle (such as acoustic neuroma)
- Infratemporal bone
- External auditory canal
- Parotid gland
- Peripheral nerve lesions
- Infratemporal bone tumors
- External auditory canal tumors
- Parotid gland tumors
- Facial nerve schwannoma
- Lymphoma
Inflammatory
- Sarcoidosis (Heerfordt syndrome)
- Vasculitis
Miscellaneous
- A number of other etiologies of facial nerve paralysis are documented including
- Congenital facial paralysis (Mobius syndrome)
- Diabetes
- Guillain-Barre syndrome
- Melkersson-Rosenthal syndrome
- Infarction
- Pontine demyelination
Epidemiology
Bell's palsy accounts for about 50% of facial nerve palsies.
- Affects 1 in 60–70 people in a lifetime
- Peaks between the ages of 10 and 40
- Affects men and women equally
Trauma accounts for about 25% of facial nerve palsies.
Lyme disease accounts for about 10% of facial nerve palsies.
History
Observation warranted if
- Classic viral prodrome
- Rapid onset
- Partial unilateral palsy
- Present less than 3 to 4 weeks
Imaging recommended if
- Palsy lasts greater than 3 to 4 weeks
- Complete paralysis
- Gradual onset
- Multiple cranial nerves are involved
Clinical features
Facial nerve palsy most commonly presents as an acute onset of unilateral facial weakness or loss of facial expression including
- Loss of forehead wrinkling
- Brow ptosis
- Incomplete eyelid closure
- Drooping of the mouth with possible drooling
- There can be associated
- Pain around the jaw or behind the ear
- Headaches
- Changes in
Common ocular signs of facial nerve palsy
- Upper eyelid retraction
- Lower eyelid paralytic ectropion and laxity with widening of the palpebral fissure
- Lagophthalmos
- Incomplete blink
- Corneal exposure keratopathy
- Punctate epitheliopathy
- Corneal pannus
- Thinning
- Corneal ulceration
Aberrant facial nerve innervation
In longstanding or recovering facial nerve palsies, most commonly Bell's palsy, aberrant innervation can occur in 3 forms.
- Hypertonicity occurs as the affect side appears contracted at rest despite decreased dynamic function.
- Synkinesis involves regenerating axons reinnervating different muscles than those originally served, for example:
- Movements of the lower face can cause eyelid closure.
- Blinking can cause mouth twitching.
- Gustatory lacrimation ("crocodile tears"): Fibers to the sublingual and mandibular glands reinnervate the lacrimal gland causing tearing during chewing.
All 3 forms have been successfully treated with the use of botulinum toxin.
Testing
Diagnosis is made based on the presence of characteristic physical exam findings as listed above.
Observation is warranted in the setting of a classic viral prodrome with rapid onset of partial unilateral palsy present for less than 3 weeks.
Although practice patterns vary, further evaluation including imaging is recommended if multiple cranial nerves are involved or the palsy
- Progresses over a period of 3 weeks
- Is complete in nature
- Has a gradual onset
Corneal sensation should be checked in all patients with facial nerve palsy to ensure there is no involvement of CN V, which portends a worse prognosis for exposure keratopathy and requires additional work-up to determine etiology.
The presence or absence of Bell's phenomenon should be noted.
The extent of voluntary closure of the eyelids should be noted by having the patient forcibly close the eyelids and observing the extent to which the eyelashes are buried.
The ocular surface should be assessed using Schirmer and fluorescein testing because facial nerve palsy exceeding 3 months in duration can result in a loss of parasympathetic tear stimulation and altered meibomian gland morphology.
Testing for staging, fundamental impairment
Grading of facial nerve palsy can be performed using the House-Brackman guide:
