Bell's Palsy

Acute, idiopathic, unilateral peripheral facial nerve (CN VII) palsy, presumed due to viral reactivation (most implicated: HSV-1, also VZV) causing inflammation, edema, and compression of the nerve within the narrow bony facial canal (labyrinthine segment is narrowest point).

Most common cause of acute facial paralysis (~60–75% of cases).

Diagnosis of exclusion.

Classified by:

• Not formally subtyped, but distinguished by grading of severity ; House-Brackmann scale (Grade I normal to Grade VI complete paralysis) ; used for prognostication and monitoring recovery

• Distinguish from other causes of facial palsy grouped as: idiopathic (Bell's palsy), infectious (Ramsay Hunt/VZV, Lyme disease, otitis media, HIV), traumatic, neoplastic (parotid tumor, cerebellopontine angle tumor, facial nerve schwannoma), other (Guillain-Barré, sarcoidosis, diabetes mellitus, pregnancy ; increased incidence in 3rd trimester/postpartum)

• Acute onset (hours to 1–2 days), unilateral, peaks within 72 hours

• Lower motor neuron pattern; critical distinguishing feature: entire hemiface affected including forehead (unlike UMN/stroke lesions which spare the forehead due to bilateral cortical innervation of frontalis)

• Inability to raise eyebrow, close eye (lagophthalmos), flatten nasolabial fold, purse lips/smile on affected side

• Bell's phenomenon: upward eye deviation on attempted closure (normal reflex, becomes visible due to lagophthalmos)

• Associated symptoms (reflect involvement of nerve branches proximal to the lesion):

• Hyperacusis (stapedius nerve branch)

• Loss of taste anterior 2/3 tongue (chorda tympani)

• Decreased tearing or, paradoxically, excessive tearing (greater petrosal nerve/impaired drainage due to weak orbicularis oculi)

• Postauricular/ear pain (often precedes palsy by 1-2 days)

• Numbness/heaviness sensation on affected side (subjective, sensory exam usually objectively normal ; true sensory loss suggests alternative diagnosis)

• Red flags suggesting alternative diagnosis (NOT Bell's palsy):

• Gradual onset over weeks (suggests tumor ; parotid mass, acoustic neuroma, cholesteatoma)

• Bilateral facial weakness (Guillain-Barré, sarcoidosis, Lyme disease, bilateral Bell's is rare)

• Vesicles in ear canal/pinna/palate (Ramsay Hunt syndrome; VZV reactivation, worse prognosis)

• Other cranial neuropathies or limb weakness/ataxia (brainstem stroke, tumor)

• Parotid mass or facial twitching preceding palsy (parotid malignancy)

• Recurrent ipsilateral or alternating palsy (consider sarcoidosis, tumor)

• History of tick exposure/erythema migrans rash/endemic area (Lyme disease)

Clinical diagnosis; no routine investigations needed in typical presentation with no red flags.

Investigate selectively if atypical features present:

• MRI brain with contrast (internal auditory canal/cerebellopontine angle protocol): if gradual onset, bilateral, other neurological signs, or no improvement/worsening after 3–4 months ; excludes tumor, stroke, MS

• Lyme serology: if endemic area, tick exposure, rash, bilateral palsy

• VZV serology/PCR if vesicles present (Ramsay Hunt)

• Blood glucose/HbA1c: diabetes associated with higher incidence and poorer recovery

• Electrodiagnostic testing (electroneurography/EMG): if complete paralysis, to help predict prognosis and guide surgical decompression discussion (rarely used)

Differentials: stroke (UMN pattern ; forehead spared; other neuro deficits), Ramsay Hunt syndrome, Guillain-Barré syndrome (bilateral, ascending weakness, areflexia), Lyme disease, acoustic neuroma/CPA tumor, parotid malignancy, otitis media/mastoiditis, multiple sclerosis, sarcoidosis (bilateral, uveoparotid fever), HIV, trauma (temporal bone fracture).

• Eye protection; mandatory, prevents exposure keratopathy/corneal ulceration (most important preventable complication):

• Artificial tears (lubricating drops) hourly while awake

• Lubricating ointment + eye patch/taping shut at night

• Wraparound sunglasses during day

• Corticosteroids ; first-line, most benefit if started within 72 hours of onset:

• Prednisolone 50–60mg PO od for 10 days (or 60mg for 5 days then taper over 5 days); improves rate and completeness of recovery

• Antivirals; adjunct, evidence weaker alone but often combined with steroids, especially in severe palsy (House-Brackmann IV–VI) or suspected Ramsay Hunt:

• Aciclovir 400mg 5x/day for 7–10 days, or valaciclovir 1g PO tds for 7 days

• For confirmed Ramsay Hunt: valaciclovir + prednisolone, higher-dose regimens sometimes used

• Analgesia for associated pain (paracetamol, NSAIDs)

• Facial physiotherapy: may help, particularly for synkinesis prevention in moderate-severe cases; evidence modest

• Surgical decompression: rarely indicated, reserved for cases with >90% degeneration on electroneurography within 2 weeks and no voluntary motor unit potentials on EMG; controversial, specialist ENT/neurosurgical decision

Prognosis: ~70% recover fully without treatment; treatment improves this further. Most improvement begins within 3 weeks; full recovery typically by 3–6 months. Poor prognostic factors: complete paralysis at onset, older age, diabetes, hyperacusis, severe pain, delayed treatment initiation.

Complications if untreated/severe: exposure keratopathy, corneal ulceration, synkinesis (aberrant reinnervation causing involuntary movements), crocodile tears syndrome (gustatory lacrimation), persistent weakness (~15–30% incomplete recovery in untreated cases).

Referral: ophthalmology if corneal complications; ENT/neurology if atypical features, no improvement by 3–4 months, or recurrent/bilateral palsy.