What feature is most consistent with a central lesion in a patient with slurred speech, right-sided facial drooping, ptosis of the right eye, loss of the right nasolabial fold, and symmetric wrinkling of the forehead with raising eyebrows?

Central vs Peripheral Facial Palsy: Identifying Central Lesions

The symmetric wrinkling of the forehead with raising eyebrows is the feature most consistent with a central lesion in this patient with right-sided facial weakness.

Understanding Central vs Peripheral Facial Nerve Lesions

Central (supranuclear) and peripheral (nuclear or infranuclear) facial nerve lesions present with distinct clinical patterns due to differences in neural pathway organization:

Central Lesion Characteristics

• Forehead sparing: Symmetric forehead wrinkling when raising eyebrows
• Affects lower face predominantly (mouth, cheek)
• Contralateral to the brain lesion
• Often accompanied by other neurological deficits

Peripheral Lesion Characteristics

• Complete facial weakness (upper and lower face)
• Asymmetric forehead wrinkling
• Inability to close eye completely
• Ipsilateral to the lesion

Why Forehead Sparing Indicates a Central Lesion

The key distinguishing feature in this case is the symmetric forehead wrinkling despite facial weakness. This occurs because:

• The upper face (forehead) receives bilateral cortical innervation, meaning both hemispheres control forehead muscles
• The lower face receives only contralateral cortical innervation
• In central lesions, the intact hemisphere can still activate forehead muscles, preserving function
• In peripheral lesions, all ipsilateral facial muscles are affected, including the forehead

Additional Features Supporting a Central Lesion

Several other findings in this patient suggest a central rather than peripheral lesion:

• Slurred speech: Indicates involvement of other central nervous system pathways
• Ptosis with preserved pupillary constriction: The combination suggests central involvement rather than a peripheral cranial nerve issue
• Loss of nasolabial fold: Classic finding in central facial weakness

Clinical Reasoning Algorithm

When evaluating facial weakness, follow this approach:

1. Assess forehead movement (symmetric = central, asymmetric = peripheral)
2. Check for associated neurological symptoms (speech, motor, sensory)
3. Evaluate eye closure and other facial movements
4. Test pupillary responses and other cranial nerves

Common Pitfalls to Avoid

• Mistaking ptosis for eye closure weakness: In this case, the ptosis with preserved pupillary function suggests central involvement
• Focusing only on the side of weakness: Remember to compare with the unaffected side
• Overlooking associated symptoms: The slurred speech is a critical clue pointing to a central process
• Incomplete testing: Always test forehead movement specifically when evaluating facial weakness

The patient's presentation with right-sided facial weakness but preserved forehead wrinkling, along with slurred speech, strongly indicates a central (likely left hemispheric) lesion affecting the corticobulbar tract.