Can a stroke of the precentral gyrus (primary motor cortex) in an older adult with hypertension, diabetes, and dyslipidemia cause a true peripheral facial palsy?

Can a Precentral Gyrus Stroke Cause Peripheral Facial Palsy?

No, a stroke of the precentral gyrus (primary motor cortex) cannot cause a true peripheral facial palsy—it produces a central facial palsy that spares the forehead.

Fundamental Neuroanatomical Distinction

The critical difference lies in the anatomical pathway of facial nerve innervation:

• Central facial palsy (from precentral gyrus or corticonuclear tract lesions) affects only the lower face because the upper facial muscles receive bilateral cortical innervation, leaving forehead movement intact 1, 2
• Peripheral facial palsy (from facial nerve or nucleus lesions) affects both upper and lower face equally, including inability to close the eye or wrinkle the forehead 3, 4

This distinction is the cornerstone of clinical diagnosis and determines whether neuroimaging is required 5.

Clinical Presentation of Precentral Gyrus Stroke

A precentral gyrus infarction produces isolated central facial palsy with these specific features:

• Weakness limited to the contralateral lower face (mouth, lower cheek) 1
• Preserved forehead function—the patient can wrinkle their forehead and close their eye completely 2
• Often subtle and may be mistaken for habitual facial asymmetry 1
• Typically NIHSS scores of 1-2 when isolated 1

In a study of 5,169 stroke patients, only 4 (0.08%) presented with isolated central facial palsy from corticonuclear tract lesions, demonstrating how rare and easily missed this presentation can be 1.

When Central Lesions Mimic Peripheral Palsy

Critical pitfall: Pontine lesions affecting the facial nerve nucleus or fascicles can produce true lower motor neuron facial palsy that mimics Bell's palsy 6, 5:

• A 75-year-old woman with unilateral upper and lower facial weakness was ultimately diagnosed with pontomedullary junction stroke affecting facial nerve fascicles 6
• A 36-year-old man initially treated for peripheral vertigo had pontine infarction at the facial colliculus, producing LMN facial palsy 5

However, these are NOT precentral gyrus strokes—they are brainstem lesions affecting the facial nerve nucleus itself before it exits the brainstem 6, 5.

Red Flags Requiring Neuroimaging

Any patient with "peripheral-appearing" facial palsy should undergo brain MRI if:

• Other neurological symptoms are present (vertigo not responding to treatment, diplopia, dysarthria, ataxia) 5
• Other cranial nerve deficits develop 5
• Young patient without typical Bell's palsy risk factors 5
• Symptoms progress or fail to improve with standard treatment 5

The presence of LMN facial palsy with any associated neurological signs warrants immediate imaging to exclude stroke or space-occupying lesions 5.

Quality of Life Impact

Central facial palsy significantly impacts quality of life despite being "minor" by NIHSS criteria 2:

• Median Facial Disability Index score was 46.5 (out of 100) at rehabilitation admission 2
• Patients with right hemispheric infarction had significantly worse lower face activation compared to left hemispheric strokes 2
• Specific muscle activation patterns (zygomaticus major, levator anguli oris, orbicularis oris) improved with targeted rehabilitation 2

Rehabilitation focusing on specific facial muscle groups should be part of post-stroke care, as 79% of patients had House-Brackmann grade ≥III facial weakness requiring intervention 2.

Diagnostic Algorithm

For a patient presenting with unilateral facial weakness:

1. Assess forehead function immediately 3, 4

   • Can they wrinkle forehead? Can they close eye completely?
   • If YES → Central palsy → Stroke workup mandatory
   • If NO → Peripheral palsy → Consider Bell's palsy vs. other causes

2. If peripheral pattern, assess for stroke mimics 6, 5:

   • Any other cranial nerve findings?
   • Vertigo, ataxia, diplopia, dysarthria?
   • If YES → Brain MRI with DWI urgently

3. If isolated peripheral palsy without red flags 3:

   • Diagnosis of exclusion (Bell's palsy)
   • No routine imaging or laboratory testing needed
   • Consider Lyme serology only in endemic areas

Answer to Your Specific Clinical Scenario

In your older adult with hypertension, diabetes, and dyslipidemia:

• A precentral gyrus stroke would produce lower face weakness only with preserved forehead function 1
• This is NOT a peripheral facial palsy by definition 4
• If the patient has true upper and lower face involvement, consider pontine stroke affecting the facial nucleus rather than cortical stroke 6, 5
• The vascular risk factors increase stroke probability, making neuroimaging essential if any atypical features are present 5, 1