Which finding helps differentiate a lower motor neuron facial nerve palsy from an upper motor neuron lesion?

Which finding helps differentiate a lower motor neuron facial nerve palsy from an upper motor neuron lesion?

• A. Involvement of forehead
• B. Forehead sparing
• C. Bilateral weakness
• D. Eyelid droop

Answer: (B)

Forehead sparing indicates an upper motor neuron pattern. The muscles of the forehead receive input from both hemispheres, so a UMN lesion causes weakness of the opposite lower face while the forehead can still move. In contrast, a lower motor neuron palsy of the facial nerve affects the entire ipsilateral face, including the forehead. So the presence of forehead sparing helps differentiate a UMN lesion from a peripheral LMN facial nerve palsy.

Forehead sparing indicates an upper motor neuron pattern. The muscles of the forehead receive input from both hemispheres, so a UMN lesion causes weakness of the opposite lower face while the forehead can still move. In contrast, a lower motor neuron palsy of the facial nerve affects the entire ipsilateral face, including the forehead. So the presence of forehead sparing helps differentiate a UMN lesion from a peripheral LMN facial nerve palsy.