In an older adult with vascular risk factors, can a stroke affecting the precentral gyrus cause facial palsy?

Can Precentral Gyrus Stroke Cause Facial Palsy?

Yes, a stroke affecting the precentral gyrus (primary motor cortex) can cause facial palsy, but it presents as central facial palsy with characteristic upper facial sparing—though recent evidence shows upper facial weakness occurs in 76% of cases, challenging traditional teaching. 1

Key Distinguishing Features of Central vs. Peripheral Facial Palsy

Central Facial Palsy (Stroke-Related)

• Traditionally spares forehead muscles, allowing patients to wrinkle forehead, raise eyebrows, and close eyes completely, though this is not absolute 2
• Recent evidence contradicts classical teaching: 76% of acute ischemic stroke patients with central facial palsy demonstrate upper facial weakness, with tight eye closure being the most sensitive indicator (42% show asymmetry) 1
• Lower facial weakness predominates, affecting ability to smile or purse lips on the contralateral side 2
• Accompanied by other neurological deficits such as limb weakness, speech difficulties, dizziness, dysphagia, or diplopia 2, 3
• Stroke severity (higher NIHSS scores) and presence of lower facial weakness predict upper facial involvement (adjusted OR 1.42 and 6.56, respectively) 1

Peripheral Facial Palsy (Bell's Palsy)

• Complete hemifacial weakness including forehead with inability to raise eyebrows or close eye on affected side 2, 3
• Isolated facial nerve involvement without other cranial nerve or limb deficits 2, 3
• Rapid onset within 72 hours is cardinal feature 3, 4
• Associated symptoms: taste disturbance (anterior 2/3 tongue), hyperacusis, dry eye, ear pain 2, 3

Critical Diagnostic Approach in Vascular Risk Patients

Immediate Red Flags Requiring Stroke Workup

• Any additional neurological symptoms beyond isolated facial weakness mandate stroke evaluation 2, 3
• Document all cranial nerves systematically: involvement of CN V, VI, VIII, IX, X, XI, or XII excludes Bell's palsy and indicates central pathology 3
• Assess for limb weakness, speech disturbance, altered mental status, gaze deviation 2
• Use NIHSS scoring to quantify deficits and facilitate communication 2

Anatomical Localization

• Precentral gyrus lesions affect the corticofacial pathway (upper motor neuron), producing contralateral facial weakness 1, 5
• Pontine lesions affecting facial nucleus can produce ipsilateral peripheral-type facial palsy, though usually with additional brainstem signs 2
• Rare presentations exist: frontal lobe ischemic stroke can mimic peripheral facial palsy, creating diagnostic challenges 6

Imaging and Workup Algorithm

When Stroke is Suspected (Vascular Risk Factors + Facial Palsy)

1. Immediate non-contrast CT head to exclude hemorrhage and identify large vessel occlusion 2
2. MRI brain with diffusion-weighted imaging is more sensitive for acute ischemia, particularly cortical and small vessel strokes 2
3. Vascular imaging (CT angiography or MR angiography) to identify large vessel occlusion if intervention candidate 2
4. Laboratory tests: glucose, electrolytes, CBC, coagulation studies, cardiac markers 2

When Bell's Palsy is Suspected (Isolated Facial Weakness)

• No routine imaging required for typical presentation with rapid onset <72 hours and no other neurological findings 2, 3
• Image only if: symptoms persist >2 months, atypical presentation, recurrent episodes, or any other cranial nerve involvement 2, 3
• MRI orbit/face/neck with contrast plus brain MRI is gold standard when imaging indicated 2, 3

Common Pitfalls to Avoid

Misdiagnosing Stroke as Bell's Palsy

• Assuming forehead sparing is absolute: 76% of central facial palsy patients show upper facial weakness, though typically milder than lower face 1
• Failing to assess other neurological functions: always document limb strength, speech, cranial nerves, and mental status 2, 3
• Overlooking subtle brainstem signs: pontine infarcts can rarely present with isolated facial palsy 2
• Missing cortical stroke: frontal lobe infarction can present with peripheral-type facial palsy pattern 6

Misdiagnosing Bell's Palsy as Stroke

• Over-imaging typical Bell's palsy: patients with classic presentation (rapid onset <72 hours, complete hemifacial weakness including forehead, no other deficits) do not require imaging 2, 3
• Delaying corticosteroid treatment: Bell's palsy requires prednisolone 50mg daily for 10 days or prednisone 60mg daily for 5 days with taper, ideally within 72 hours 3, 7

Quality of Life and Prognostic Considerations

Central Facial Palsy (Stroke)

• Significant impact on quality of life: median Facial Disability Index score of 46.5 and FaCE score of 69 in stroke patients 5
• Improvement with rehabilitation: specific facial muscle exercises targeting action units (zygomaticus major, levator anguli oris, orbicularis oris) show benefit 5
• Functional impairments: reduced masticatory performance, dysphagia, facial asymmetry affect nutrition and social function 8, 5

Peripheral Facial Palsy (Bell's Palsy)

• Generally favorable prognosis: 83% recovery at 3 months with corticosteroids vs 63.6% with placebo 3
• Risk of permanent complications: 30% may experience persistent facial weakness with contracture 4
• Corneal protection mandatory: lagophthalmos can cause permanent corneal damage requiring lubricating drops, ointment, and eye taping 3, 4

Definitive Recommendation

In an older adult with vascular risk factors presenting with facial palsy, perform immediate systematic neurological examination including all cranial nerves, limb strength, speech, and mental status. 2, 3 If any additional neurological deficit is present or upper facial muscles are relatively spared compared to lower face, treat as stroke until proven otherwise with urgent non-contrast CT and consideration for thrombolysis. 2, 1 If examination reveals isolated complete hemifacial weakness including forehead with rapid onset <72 hours and no other deficits, diagnose Bell's palsy and initiate corticosteroids immediately without imaging. 2, 3