Is this an upper or lower motor neurone lesion?
The animation demonstrates the difference in facial weakness between an upper or a lower motor neurone lesion.
The key to differentiating a central (upper motor neurone) from a peripheral (lower motor neurone) facial palsy is to identify the extent of facial muscle weakness.
The muscles of the upper half of the face (frontalis, corrugator and orbicularis) are innervated bilaterally by corticobulbar fibres. Weakness of the forehead muscles indicates a peripheral facial nerve problem, whereas sparing of the forehead muscles is diagnostic of a central lesion.
Asking the patient to close their eyes tightly or wrinkle their forehead will quickly identify the source of the problem.
Having identified a peripheral facial muscle weakness, the clinician must then exclude other causes before diagnosing an idiopathic palsy (Bell’s palsy).
Learning bite
A patient with facial weakness who cannot close their eye tightly or raise their eyebrow has a peripheral facial palsy.