Bell Palsy

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

• Peripheral Facial Nerve Dysfunction: Bell palsy specifically refers to idiopathic, unilateral paresis or paralysis of the facial nerve (Cranial Nerve VII). Cranial nerve VII supplies motor innervation to the muscles of facial expression, the scalp, and the stapedius muscle, as well as sensory taste fibers to the anterior two-thirds of the tongue.
• Viral-Induced Mechanical Entrapment: The prevailing pathophysiological mechanism is localized inflammation and edema of the facial nerve. Herpes simplex virus (HSV) DNA and antigens have been isolated around the facial nerve in affected patients, suggesting a viral or post-viral reactivation that leads to nerve sheath swelling. Because the facial nerve traverses a narrow, rigid bony canal (the facial canal), any secondary swelling causes mechanical compression, ischemia, and subsequent axonal block.
• The Upper Motor Neuron (UMN) vs. Lower Motor Neuron (LMN) Anatomy: Clinicians must understand the neuroanatomy of the facial nucleus to localize the lesion. The lower facial muscles are innervated solely by contralateral corticobulbar fibers, whereas the upper facial muscles (forehead) receive bilateral crossed cortical innervation.
• Central (UMN) Lesions (e.g., Cortical Stroke): Spares the forehead because the ipsilateral crossed fibers from the unaffected hemisphere preserve forehead motor function.
• Peripheral (LMN) Lesions (e.g., Bell Palsy): Affects the facial nerve nucleus or the nerve itself, interrupting all motor pathways. This results in flaccid weakness of the entire ipsilateral side of the face, including the forehead.

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Airway and Breathing Stabilization: Isolated 7th cranial nerve neuropathies should not cause airway, breathing, or hemodynamic compromise. If a patient exhibits respiratory distress, dysphagia, or hemodynamic instability, the clinician must immediately abort the diagnosis of Bell palsy and evaluate for life-threatening central pathologies, such as a brainstem stroke, elevated intracranial pressure (ICP), or meningitis.
• First-Line Pharmacotherapy (Corticosteroids): Corticosteroids improve outcomes and must be initiated as soon as possible, ideally within 72 hours of symptom onset. Select one of the following regimens:
• Prednisone: 60 to 80 mg/day PO for 1 week.
• Prednisolone: 1 mg/kg/day PO for 7 to 10 days.
• Methylprednisolone: 1 mg/kg/day PO every 24 hours for 7 to 10 days.
• Antiviral Adjunctive Therapy: While isolated antiviral treatment does not improve outcomes, adding antivirals to steroids is recommended, especially in moderate-to-severe cases of facial paralysis. Administer within 72 hours of onset:
• Valacyclovir: 1,000 mg (1 g) PO 3 times daily for 1 week.
• Acyclovir: 400 mg PO 5 times daily for 1 week.
• Aggressive Ophthalmic Care: Inability to fully close the eyelid (lagophthalmos) puts the patient at high risk for exposure keratitis, corneal drying, and permanent corneal ulceration.
• Prescribe artificial tears or medicated eye drops to be used several times during the day.
• Prescribe a thick ophthalmic ointment and apply a protective occlusive shield at night.
• Direct the patient to seek immediate medical evaluation if they develop eye pain or a red eye.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

Top Mimics to Exclude

1. Brainstem (Pontine) Stroke: Approximately 1% of new facial palsies are actually pontine strokes. An ischemic infarct affecting the CN VII nucleus in the pons will cause a peripheral-pattern facial palsy that includes the forehead. Differentiate by checking for coexisting abducens (CN VI) palsy (ipsilateral lateral gaze deficit) and contralateral extremity weakness or sensory loss (crossed hemiplegia).
2. Ramsay Hunt Syndrome (Herpes Zoster Oticus): Characterized by severe retroauricular pain, facial paralysis, and vesicular lesions in the external auditory canal or hard palate.
3. Lyme Disease: Lyme disease can cause unilateral or bilateral facial nerve palsy. Bilateral facial palsy (facial diplegia) is highly unlikely to be Bell palsy and must prompt immediate evaluation for Lyme disease, sarcoidosis, Guillain-Barré syndrome, or Myasthenia Gravis.
4. Compressive Mass (Parotid Gland or Salivary Gland Tumors): These present with a more insidious onset (progressing over weeks rather than hours to 72 hours) and may have a palpable mass or associated cervical lymphadenopathy.

Prioritized Workup Strategy

• Physical Exam First: The diagnosis of Bell palsy remains a clinical diagnosis of exclusion based on a detailed head, neck, and cranial nerve examination.
• Routine Lab Testing: Routine lab tests are not necessary to manage Bell palsy from the ED.
• Lyme Serology: Indicated in patients living in or traveling to Lyme-endemic areas, or with a known history of a tick bite.
• Special Cohort Screening (French Guidelines): Consider a complete blood count and Hemoglobin A1c in diabetic patients, and HIV screening if clinically indicated.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• Routine Neuroimaging Restriction: No neuroimaging (CT or MRI) is indicated for patients with a classic, straightforward presentation of Bell palsy.
• CT Brain Indications: A non-contrast head CT is indicated only if the facial paralysis spares the forehead (indicating a central stroke) or if there is an inability to abduct the eye (indicating a CN VI abducens nucleus lesion).
• Contrast-Enhanced MRI of the Brain & Parotid: Consider organizing this within 1 month if the patient exhibits atypical signs, has made no clinical improvement within 3 weeks, or has no resolution of symptoms at 4 months.
• Diagnostic Otoscopy Visuals:
• External Canal & Hard Palate: Systematically inspect for vesicles (Ramsay Hunt syndrome) or granulation tissue in the external canal (necrotizing external otitis).
• Middle Ear: Evaluate the tympanic membrane; middle ear infections can cause secondary facial paralysis, which is a critical complication of otitis media in children.

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• House-Brackmann Scale: This is the standardized, validated clinical scale used to classify the baseline severity of facial nerve dysfunction, monitor clinical progression, and track functional recovery over time.
• The ROSIER Score (Rule of Stroke in the Emergency Room): A validated bedside tool to rapidly distinguish acute stroke from mimics. Facial weakness contributes +1 point. Any patient with a positive score and an atypical pattern (such as forehead sparing) must be triaged as an acute stroke.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• The "Forehead-Sparing" Central Trap: Mistaking a central UMN deficit (stroke) for a benign Bell palsy. Sparing of the forehead is a central stroke until proven otherwise.
• The "Pons Infarct" Mimic Pitfall: Failing to recognize that a pontine stroke can directly mimic Bell palsy by causing a peripheral-pattern facial palsy (including the forehead). Trainees must perform a complete cranial nerve exam, specifically testing lateral eye gaze to rule out an associated abducens (CN VI) palsy.
• Objective Facial Numbness: Bell palsy is a purely motor neuropathy; while patients may report subjective hyperesthesia, they must not have objective facial numbness. Objective sensory loss indicates involvement of Cranial Nerve V (Trigeminal) or a central stroke.
• Missed Bilateral Diplegia: Discharging a patient with bilateral facial palsy as "bilateral Bell palsy" is a critical error. Bilateral involvement is a red flag for systemic pathologies (Lyme disease, Guillain-Barré, Myasthenia Gravis).
• Critical Actions Required by Board Examiners:
• Document a baseline visual acuity on every patient presenting with eye-closure deficit.
• Explicitly inspect the external ear canal and hard palate for shingles vesicles.
• Instruct the patient to wrinkle the forehead to differentiate central vs. peripheral lesions.
• Initiate steroids within 72 hours of symptom onset.

7. MCQ MASTERCLASS (Written Exam Tips)

• The Forehead Rule: Forehead spared = Central (Stroke). Forehead involved = Peripheral (Bell palsy or brainstem pontine stroke).
• The 1% and 0.8% Statistics: 1% of new facial palsies are pontine strokes. Additionally, 0.8% of patients discharged from the ED with a diagnosis of Bell palsy are subsequently found to have a missed ischemic stroke or intracranial hemorrhage.
• The 1 in 400 Rule: Approximately 1 in 400 ED diagnoses of Bell palsy is actually a missed pontomedullary stroke.
• High-Yield Proximal Signs: Retroauricular pain, hyperacusis (secondary to stapedius muscle paralysis), and dysgeusia (loss of taste on the anterior two-thirds of the tongue) localize the lesion proximally within the facial canal.
• The Bell Phenomenon: When attempting to close the eyes, the eyeball on the paralyzed side rolls upward, leaving the white sclera visible. This is a reassuring peripheral sign.
• Antiviral Monotherapy Distractor: Do not select antiviral monotherapy on a multiple-choice question; isolated antiviral treatment provides no clinical benefit over corticosteroids.

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• Triage and Initial Assessment: "On arrival of this patient with acute unilateral facial weakness, I am securing the primary survey. I note that isolated 7th cranial nerve neuropathies do not cause airway or hemodynamic compromise. If any respiratory or circulatory distress is present, I will immediately abort the diagnosis of Bell palsy and evaluate for a brainstem stroke, meningitis, or elevated ICP."
• Focused Physical Examination: "I will perform a focused neurological and cranial nerve examination. I will instruct the patient to 'raise your eyebrows' and 'close your eyes tightly against resistance'. If the forehead is involved, this confirms a peripheral CN VII pattern. I will meticulously test lateral eye gaze to exclude a CN VI abducens palsy and check the extremities for crossed motor or UMN signs to rule out a pontine stroke mimic."
• Systematic Head and Neck Exam: "I will perform otoscopy to inspect the tympanic membrane for middle ear infections and the external canal for shingles vesicles. I will inspect the hard palate for Ramsay Hunt syndrome, and palpate the parotid glands to rule out compressive tumors or abscesses. I will also check and document the patient's visual acuity."
• Resuscitative and Discharge Plan: "Since this is a classic, peripheral Bell palsy presenting within 72 hours, I will prescribe Prednisone 60 to 80 mg PO daily for 1 week and Valacyclovir 1,000 mg PO three times daily for 1 week. I will initiate aggressive eye care with artificial tears during the day, a thick ointment at night, and a protective occlusive eye shield. I will discharge the patient to follow up with their primary care physician and ophthalmology."