A 40-year-old male presents with acute onset of unilateral facial weakness. He cannot close his right eye, his right nasolabial fold is flattened, and...

Question

A 40-year-old male presents with acute onset of unilateral facial weakness. He cannot close his right eye, his right nasolabial fold is flattened, and his right forehead is smooth (unable to wrinkle). He has no other neurological deficit. What is the key clinical feature that distinguishes this as a lower motor neurone (LMN) lesion rather than an upper motor neurone (UMN) lesion such as stroke?

Accepted Answer

Involvement of the forehead - LMN CN VII palsy affects ALL branches (including the forehead), whereas UMN lesions spare the forehead because of bilateral cortical innervation of the upper face

Answer

Eye closure difficulty is only seen in UMN lesions

Answer

LMN lesions always cause bilateral facial weakness

Answer

The speed of onset distinguishes LMN from UMN lesions

Answer

Taste disturbance differentiates UMN from LMN lesions

uk-dipimc MCQ (SBA): LMN vs UMN Facial Weakness