Facial Nerve Palsy

Facial nerve palsy is weakness or paralysis of the muscles of facial expression. The key clinical distinction is between upper motor neuron lesions, which spare the forehead because of bilateral cortical innervation, and lower motor neuron lesions, which affect the entire hemiface. Annual incidence of peripheral facial palsy is about 20 to 30 per 100,000.

Anatomy of the lower motor neuron pathway

• The motor nucleus lies in the caudal pons, and the nerve loops around the abducens nucleus before exiting at the cerebellopontine angle with the vestibulocochlear nerve.
• It travels through the internal acoustic meatus and the facial canal: labyrinthine, geniculate ganglion, tympanic, and mastoid segments.
• Branches in the canal supply lacrimation (greater petrosal nerve), the stapedius muscle, and taste from the anterior two thirds of the tongue (chorda tympani).
• It exits at the stylomastoid foramen, enters the parotid gland, and divides into temporal, zygomatic, buccal, marginal mandibular and cervical branches.

Causes

• Idiopathic (Bell palsy): about 60 to 70%, strongly linked to HSV-1 reactivation within the geniculate ganglion.
• Infection: varicella zoster (Ramsay Hunt syndrome), Lyme disease, HIV seroconversion, acute and chronic otitis media, mastoiditis, malignant otitis externa, and tuberculosis.
• Trauma: temporal bone fracture (longitudinal in 70 to 90% and transverse in 10 to 30%), iatrogenic injury during parotid, ear or skull base surgery, facial lacerations, and birth injury.
• Neoplasm: acoustic neuroma and other cerebellopontine angle tumours, facial nerve schwannoma, parotid malignancy, cholesteatoma, and leukaemic infiltration.
• Neurological and systemic: stroke, multiple sclerosis, Guillain-Barré syndrome (often bilateral), sarcoidosis (including Heerfordt syndrome), diabetes, pregnancy, and Melkersson-Rosenthal syndrome.
• Congenital: Moebius syndrome, hemifacial microsomia, CHARGE syndrome.

Recovery depends on the cause. In Bell palsy, about 70 to 85% recover completely, with incomplete palsies recovering in over 90% and complete palsies in 60 to 70%. Poor prognostic indicators are complete paralysis, age over 60, diabetes, hypertension, severe pain, and absent recovery by 3 weeks.

Lower motor neuron signs

• Inability to wrinkle the forehead, raise the brow, or close the eye. On attempted closure the eye rolls upward (Bell phenomenon).
• Flat nasolabial fold, drooping corner of the mouth, drooling, food collecting in the cheek, and difficulty with whistling or puffing.
• Eye dryness or epiphora, and exposure keratopathy.

Level localisation

• Lesion at the cerebellopontine angle or internal meatus: hearing loss, tinnitus, vertigo, reduced lacrimation, taste loss, and hyperacusis.
• Above the geniculate ganglion: reduced tear production in addition to the features below.
• Between the geniculate ganglion and the stapedius nerve: hyperacusis plus taste loss.
• Between the stapedius and chorda tympani: taste loss and reduced salivation only.
• At the stylomastoid foramen or distal: isolated facial weakness.

Severity is graded on the House-Brackmann scale (I normal, II slight weakness, III obvious but not disfiguring with complete eye closure, IV incomplete eye closure, V barely perceptible movement, VI no movement).

Associated findings

• Postauricular pain precedes weakness in half of Bell palsy cases.
• Vesicles in the ear canal, concha or palate, with sensorineural deafness and vertigo, indicate Ramsay Hunt syndrome.
• Expanding parotid mass, skin cancer, or neck mass suggests malignancy.
• Erythema migrans, tick exposure and bilateral involvement suggest Lyme disease.
• Hemiparesis, arm or leg weakness, or speech difficulty suggest a central cause.

Red flags prompting investigation beyond the clinical diagnosis

• Slow progression over more than 3 weeks.
• Absence of any recovery by 3 to 4 months.
• Recurrent palsy on the same side.
• Facial twitching or spasm before weakness.
• Other cranial neuropathies, hearing loss or vestibular symptoms.
• Parotid mass or skin cancer.
• Bilateral palsy.
• Forehead sparing (central cause).

Bell palsy is a clinical diagnosis of exclusion after a detailed history, ear examination, parotid and neck examination, cranial nerve and neurological examination.

Baseline tests

• Glucose or HbA1c.
• Lyme serology in endemic regions, HIV test when risk factors are present, and syphilis serology.
• Audiometry for hearing symptoms or suspected Ramsay Hunt syndrome or tumour.
• Schirmer test, stapedial reflex, and taste testing to localise the lesion when needed.

Imaging

• MRI of the brain, internal auditory canal and parotid with gadolinium in atypical, progressive or non-recovering palsy, with associated cranial neuropathies, or recurrent palsy. Enhancement of the facial nerve is common in Bell palsy and in Ramsay Hunt syndrome, so enhancement alone does not indicate tumour.
• High resolution CT of the temporal bone for trauma, chronic ear disease and suspected cholesteatoma.
• Ultrasound or MRI of the parotid for masses.

Electrodiagnostic testing quantifies degeneration

• Electroneuronography (ENoG) between days 3 and 14 compares the compound muscle action potential of the affected side with the normal side. Degeneration above 90% predicts poor recovery and identifies candidates for decompression in selected cases.
• Needle EMG at 2 to 3 weeks shows fibrillation potentials in denervated muscle. Voluntary motor unit potentials indicate a favourable prognosis.
• Blink reflex testing helps with localisation.

Eye protection (all patients with incomplete eyelid closure)

• Lubricating drops (carboxymethylcellulose 0.5% or hypromellose, every 1 to 2 hours while awake), ointment at night, and eyelid taping or a moisture chamber.
• Persistent lagophthalmos: upper lid gold or platinum weight (0.8 to 1.6 g), lower lid tightening (lateral tarsal strip), or temporary tarsorrhaphy.
• Urgent ophthalmology review for corneal abrasion, ulcer or infection.

Bell palsy

• Oral prednisolone started within 72 hours: 50 mg daily for 10 days, or 60 mg daily for 5 days then reduced by 10 mg daily over 5 days. Monitor glucose in diabetes.
• Antiviral addition (valaciclovir 1 g three times daily for 7 days) is optional and adds little. Consider it in severe palsy (House-Brackmann V to VI).
• Facial exercises and physiotherapy, with massage, have small benefit. Electrical stimulation can worsen synkinesis.

Ramsay Hunt syndrome

• Prednisolone 1 mg/kg daily (usually 60 mg) for 5 to 7 days with taper over 2 weeks, plus valaciclovir 1 g three times daily or aciclovir 800 mg five times daily for 7 to 10 days. Severe disease or immunosuppression needs IV aciclovir 10 mg/kg every 8 hours.
• Analgesia and antiemetics for vertigo.

Lyme disease

• Doxycycline 100 mg twice daily for 14 to 21 days. Use ceftriaxone 2 g IV daily for 14 to 28 days when meningitis is present.

Otitis media or mastoiditis

• IV antibiotics (for example ceftriaxone 2 g daily), myringotomy or mastoidectomy as required.

Trauma

• Immediate complete paralysis with a transverse fracture or confirmed disruption: surgical exploration and decompression or repair.
• Delayed onset paralysis with incomplete weakness: observation and steroids, with ENoG surveillance.
• Penetrating injury: explore and repair within 72 hours when the distal nerve stimulates, using tension free end to end neurorrhaphy or interposition graft (great auricular or sural nerve).

Tumours: resection or radiotherapy, with facial nerve preservation or reconstruction.

Surgical decompression

• Reserved for Bell palsy with complete paralysis, ENoG degeneration above 90% within 2 weeks, and absent voluntary EMG. Benefit is uncertain.

Chronic palsy and rehabilitation

• Reanimation within 12 to 24 months of denervation: facial nerve repair or cross facial nerve grafting, hypoglossal to facial nerve transfer or masseteric nerve transfer, and free functional gracilis muscle transfer in long standing palsy.
• Static procedures: temporalis transfer, fascia lata slings, brow lift, and eyelid procedures.
• Synkinesis and hypertonicity: botulinum toxin type A 2.5 to 5 units per site every 3 to 4 months, with neuromuscular retraining.
• Crocodile tears (gustatolacrimal reflex): botulinum toxin to the lacrimal gland, 2.5 to 5 units.

Children with Bell palsy recover well, but Lyme disease and otitis media need to be excluded. Neonatal palsy from birth trauma recovers within weeks in most cases, while persistent palsy suggests congenital absence.