Bell's Palsy

Bell Palsy – High-Yield Study Guide for Medical Students

Definition

Bell palsy is an acute, idiopathic, unilateral lower motor neuron (LMN) facial nerve (cranial nerve VII) palsy, leading to sudden-onset weakness of all muscles of facial expression on one side of the face. It is a diagnosis of exclusion after ruling out secondary causes such as stroke, tumors, otitis media, Lyme disease, and Ramsay Hunt syndrome.

Epidemiology

Bell palsy is the most common cause of unilateral facial paralysis and the most common cranial neuropathy.

• Annual incidence: approximately 15–40 per 100,000 persons.
• Peak incidence between 15–45 years, but can occur at any age.
• Affects males and females equally.
• Increased risk in pregnancy (especially 3rd trimester and early postpartum) and in patients with diabetes or recent upper respiratory tract infections.
• Most cases are unilateral and isolated; bilateral involvement is rare and should prompt evaluation for alternative causes (e.g., Guillain–Barré syndrome, sarcoidosis, Lyme disease).

Pathophysiology

Bell palsy reflects a lower motor neuron lesion of the facial nerve distal to the facial nucleus in the pons, classically at or near the facial canal in the temporal bone.

The leading hypothesis is an immune-mediated inflammatory neuropathy, often triggered by viral reactivation.

• Viral reactivation: Most commonly herpes simplex virus type 1 (HSV-1); varicella-zoster virus (VZV) also implicated. Reactivation in the geniculate ganglion leads to inflammation.
• Edema and compression: Inflammation causes edema of the facial nerve within the narrow facial canal (Fallopian canal), resulting in ischemia, demyelination, and sometimes axonal injury.
• Segmental demyelination: Disrupts conduction along motor fibers to facial muscles and parasympathetic/sensory fibers.
• LMN pattern: A LMN lesion affects both upper and lower facial muscles on the ipsilateral side, unlike an upper motor neuron lesion which typically spares the forehead due to bilateral cortical innervation.

Recovery occurs as inflammation resolves and remyelination/axonal regrowth occurs. Aberrant regeneration leads to synkinesis (e.g., involuntary eye closure with smiling).

Clinical Presentation

Classic Bell palsy presents with acute, unilateral facial weakness evolving over hours to 72 hours, without other neurologic deficits.

Key Symptoms

• Facial muscle weakness (LMN pattern):
  • Inability to wrinkle the forehead on the affected side.
  • Incomplete eye closure (lagophthalmos); weak or absent eye closure when attempting to blink.
  • Flattening of the nasolabial fold.
  • Drooping of the corner of the mouth; drooling.
  • Difficulty smiling, whistling, puffing cheeks.
• Onset: Maximal weakness typically within 48–72 hours.
• Pain and sensory symptoms:
  • Retroauricular or mastoid pain, often preceding weakness by 1–2 days.
  • Subjective facial numbness (but light touch sensation usually intact because trigeminal nerve is normal).
• Autonomic and sensory involvement (depending on lesion site):
  • Hyperacusis due to stapedius muscle paralysis (nerve to stapedius).
  • Decreased lacrimation if lesion is proximal to greater petrosal nerve.
  • Taste disturbance on anterior two-thirds of tongue (chorda tympani involvement).
  • Reduced salivation from submandibular/sublingual glands.

Red Flags Suggesting Alternative Diagnoses

The following features are atypical for idiopathic Bell palsy and should prompt evaluation for other causes (e.g., stroke, tumor, CNS infection, demyelinating disease):

• Forehead sparing (suggests upper motor neuron lesion / central facial palsy).
• Gradual or progressive onset over weeks rather than hours to days.
• Recurrent or bilateral facial palsy.
• Accompanying neurologic deficits: limb weakness, dysarthria, ataxia, diplopia, sensory loss.
• Parotid mass, otorrhea, chronic otitis media, or history of head and neck malignancy.
• Vesicular rash in the ear canal or pinna (consider Ramsay Hunt syndrome).
• Systemic features such as fever, meningismus, or weight loss.

Diagnosis

Bell palsy is a clinical diagnosis made after exclusion of other causes of facial paralysis. In a classic presentation, extensive testing is usually unnecessary.

History

• Time course: sudden onset, progression to maximal weakness over <72 hours.
• Laterality: unilateral facial involvement.
• Associated symptoms: retroauricular pain, hyperacusis, taste changes, decreased tearing or salivation.
• Ask about: recent viral illness, tick exposure (Lyme), trauma, surgery, vaccine history, pregnancy, diabetes, cancer history.
• Red flags: diplopia, dysphagia, limb weakness, numbness, vertigo, vesicular rash, constitutional symptoms.

Physical Examination

• Facial motor exam:
  • Ask patient to raise eyebrows, close eyes tightly, smile, puff cheeks, show teeth.
  • LMN pattern: weakness of both upper and lower face on one side, including inability to wrinkle forehead.
• Eye examination: Check ability to close eye, look for lagophthalmos, conjunctival injection, corneal dryness.
• Sensory/taste: Anterior tongue taste, hyperacusis, lacrimation (Schirmer test if needed).
• Otoscopic exam: Inspect ear canal and tympanic membrane for vesicles (Ramsay Hunt), otitis media, cholesteatoma.
• Neurological exam: Ensure no additional cranial nerve deficits or long tract signs.

Investigations

In typical isolated acute Bell palsy, no investigations are required.

• Laboratory tests (selective):
  • Blood glucose/HbA1c for diabetes screening.
  • Lyme serology in endemic areas or with suggestive history.
  • HIV, syphilis serology, autoimmune workup if systemic signs present.
• Imaging:
  • MRI with contrast of brain/CPA/temporal bone if onset is gradual, recurrent, bilateral, or associated with other neurologic deficits or if no improvement after several months.
  • CT temporal bone for suspected fracture, cholesteatoma, or otologic source.
• Electrodiagnostic testing (optional):
  • Nerve conduction studies and electromyography (EMG) are rarely needed acutely.
  • Useful for prognosis after 10–14 days if there is complete paralysis and no signs of early recovery.

Differential Diagnosis

• Central causes: Ischemic or hemorrhagic stroke (cortical or internal capsule), brainstem lesions (often with other cranial nerve or long tract signs). Typically forehead sparing in supranuclear lesions.
• Ramsay Hunt syndrome (herpes zoster oticus): Facial palsy with severe otalgia and vesicular rash in ear canal, on pinna, or oral mucosa; often more severe and slower to recover.
• Lyme disease: Especially in endemic areas; may cause bilateral facial palsy, associated erythema migrans, meningitis, or radiculopathy.
• Otitis media / mastoiditis / cholesteatoma: Facial palsy with ear pain, otorrhea, or chronic ear disease.
• Parotid gland tumors or schwannomas: Slowly progressive facial weakness, often with parotid mass.
• Guillain–Barré syndrome (GBS): Bilateral facial palsy with areflexia and ascending weakness.
• Sarcoidosis, leukemia/lymphoma, other inflammatory/infiltrative neuropathies.

Management

Management focuses on early corticosteroids, possible antivirals, and meticulous eye protection, plus rehabilitation as needed.

1. Corticosteroid Therapy (Cornerstone of Treatment)

High-quality evidence indicates that early oral corticosteroids improve the chances of complete recovery and reduce long-term sequelae.

• Indication: All patients with new-onset Bell palsy who present within 72 hours of symptom onset, unless contraindicated.
• Typical regimen (adult):
  • Prednisone 50–60 mg orally once daily for 5 days, followed by a taper over the next 5 days (e.g., 10 mg reduction per day) for a total of 10 days.
• Timing: Initiation within 72 hours is ideal; benefit diminishes if started later.
• Contraindications/precautions: Poorly controlled diabetes, uncontrolled hypertension, active infection, peptic ulcer disease, psychiatric history; weigh risks vs benefits.

2. Antiviral Therapy

The benefit of antivirals alone is minimal, but combination therapy with steroids may modestly reduce long-term synkinesis, especially in severe or complete palsy.

• Indications:
  • Moderate to severe facial palsy (House–Brackmann grade IV–VI), particularly if started within 72 hours.
  • High suspicion for herpetic etiology (e.g., severe pain, history of HSV/VZV), or early concern for Ramsay Hunt while rash not yet apparent.
• Common regimens (adult):
  • Acyclovir 400 mg orally five times daily for 7–10 days, or
  • Valacyclovir 1000 mg orally three times daily for 7 days (more convenient dosing).
• Combination therapy: Steroids + antivirals is often used in severe cases; steroids remain the primary evidence-based component.

3. Eye Protection (Critical in Incomplete Eye Closure)

Preventing corneal injury is a key practical priority in Bell palsy.

• Lubrication:
  • Frequent artificial tears during the day.
  • Lubricating ointment at night.
• Mechanical protection:
  • Eye patch at night or moisture chamber.
  • Taping eyelid closed during sleep if lagophthalmos present.
• Ophthalmology referral: For signs of exposure keratopathy (red eye, pain, foreign body sensation, visual changes) or severe incomplete closure.

4. Pain Management

• Retroauricular pain can be managed with NSAIDs (e.g., ibuprofen) or acetaminophen.
• Neuropathic pain is less common but may require agents like gabapentin in selected cases.

5. Rehabilitation and Long-Term Management

• Facial physiotherapy:
  • Facial muscle exercises to promote symmetry and prevent contractures.
  • Biofeedback and neuromuscular retraining to reduce synkinesis.
• Botulinum toxin injections:
  • Used in chronic cases with synkinesis or hemifacial spasm to improve symmetry and function.
• Surgical options:
  • Rarely, facial nerve decompression in carefully selected patients with severe degeneration and early presentation; evidence is limited.
  • Chronic facial reanimation procedures (e.g., cross-facial nerve grafting, muscle transfers) in irreversible paralysis.

Prognosis

• Most patients show improvement within 2–3 weeks and substantial recovery by 3–4 months.
• About 70–85% of patients achieve complete or near-complete recovery, especially if paralysis is incomplete at onset.
• Poor prognostic factors include: complete paralysis at onset, older age, severe pain, diabetes, lack of improvement by 3–4 weeks, and delayed treatment.
• Residual deficits can include mild facial weakness, synkinesis, contractures, crocodile tears (gustatory lacrimation), and chronic discomfort.

Key Clinical Pearls (High-Yield for Exams)

• LMN vs UMN: Bell palsy causes ipsilateral total facial paralysis (forehead and lower face). In contrast, a supranuclear (UMN) lesion such as an MCA stroke typically spares the forehead due to bilateral cortical input.
• Time course matters: Bell palsy is acute with progression over hours to 72 hours; more gradual onset suggests tumor or other non-idiopathic causes.
• Early steroids: Oral corticosteroids initiated within 72 hours significantly improve outcomes. In exam questions, look for a patient with acute unilateral facial paralysis and no red flags—steroids are the best initial treatment.
• Red flag: vesicular rash in ear: Think Ramsay Hunt syndrome in the presence of facial palsy plus otalgia and vesicles in the ear canal; treat with high-dose steroids plus antivirals and recognize that prognosis is generally worse than Bell palsy.
• Lyme disease clue: Bilateral facial palsy or facial palsy with meningitis-like symptoms in a tick-endemic area should prompt Lyme serology and treatment with appropriate antibiotics (e.g., doxycycline or IV ceftriaxone depending on CNS involvement).
• Eye care is non-negotiable: Always remember corneal protection in patients with incomplete eye closure; exam stems often test recognition of this practical step.
• Pregnancy association: Pregnancy (particularly 3rd trimester) and diabetes are risk factors; management still relies on steroids (weighing maternal–fetal risks), with careful glucose monitoring.
• Synkinesis: In chronic Bell palsy, aberrant reinnervation can cause involuntary movements, such as eye closure when smiling; botulinum toxin and physiotherapy can help.

Summary for Exams

Bell palsy is an acute idiopathic LMN CN VII palsy causing unilateral facial paralysis including the forehead. Diagnosis is clinical after excluding mimics, particularly stroke, Ramsay Hunt, and Lyme disease. Early oral corticosteroids (ideally within 72 hours) are the mainstay of therapy, antivirals are adjunctive in severe cases, and eye protection is essential to prevent corneal damage. Most patients recover fully within months, but a subset develop chronic deficits and synkinesis.