Neuroscience · Year 2 · from Neuroscience
Case 3: Bell's Palsy - Facial Nerve Lower Motor Neuron Lesion
Patient Presentation
Demographics: 48-year-old male
Chief Complaint: Left facial weakness noticed upon awakening this morning
History of Present Illness: A 48-year-old man woke up this morning and noticed the left side of his face felt "stiff." When he looked in the mirror, the left side of his face was drooping. He cannot close his left eye completely and has difficulty eating, with food falling from the left side of his mouth. He noticed decreased taste on the left anterior tongue. He reports mild pain behind his left ear that began yesterday. He denies hearing changes, limb weakness, numbness elsewhere, or recent illness. He has no history of diabetes or immunocompromise.
Physical Examination:
- Vital signs: Normal
- General: Well-appearing with obvious left facial asymmetry
- Neurological:
- Mental status: Normal
- Cranial nerves:
- CN VII: Complete left facial paralysis affecting BOTH upper and lower face - cannot raise left eyebrow, cannot close left eye (Bell's phenomenon present - eye rolls upward on attempted closure), flat left nasolabial fold, drooping left mouth angle
- All other cranial nerves intact including hearing (CN VIII)
- Motor, sensory, reflexes: Normal
- Gait: Normal
- Ear examination: Normal tympanic membrane; no vesicles (excluding Ramsay Hunt)
Workup:
- Clinical diagnosis based on characteristic presentation
- No imaging required for typical presentation
- Blood glucose: 95 mg/dL (normal)
- Lyme serology: Negative (patient lives in endemic area)
Diagnosis: Bell's palsy (idiopathic facial nerve palsy)
Treatment:
- Prednisone 60 mg daily for 7 days (started within 72 hours of onset)
- Eye protection: Artificial tears during day; lubricating ointment and taping eyelid closed at night
- Antiviral therapy (valacyclovir) added given moderately severe presentation
- Education on expected recovery timeline
- Follow-up in 1 week
- 80% of facial function recovered by 6 weeks; near-complete recovery by 4 months
Clinical Pearl: Bell's palsy must be distinguished from central facial weakness (stroke). In Bell's palsy (LMN lesion), the ENTIRE hemiface is weak including the forehead, because the facial nerve itself is damaged. In stroke (UMN lesion), the forehead is SPARED because the upper face receives bilateral cortical innervation - only the contralateral lower face is controlled by one hemisphere. Thus, forehead sparing suggests stroke, while forehead involvement suggests peripheral (LMN) facial nerve palsy. Bell's palsy is thought to result from herpes simplex virus reactivation causing inflammation in the facial canal.
Clinical Image
Image Description: Comparative illustration demonstrating upper motor neuron (central) facial weakness with forehead sparing versus lower motor neuron (peripheral) facial weakness with complete hemiface involvement including the forehead, illustrating the different innervation patterns.
Attribution: Image from Wikimedia Commons (https://commons.wikimedia.org/), Creative Commons Attribution-ShareAlike license.