A patient with left Bell's palsy (LMN facial palsy) has preserved forehead movements on the left. This indicates the lesion is:

• A Lower motor neuron lesion affecting only the lower facial nerve branches
• B Pontine lesion with hemifacial involvement
• C Incomplete Bell's palsy with only buccal branch involvement
• D Upper motor neuron (UMN) lesion sparing the upper face due to bilateral cortical representation ✓

Explanation

Preservation of forehead wrinkling in a facial palsy strongly indicates an upper motor neuron (UMN) lesion. The frontalis muscle has bilateral cortical representation (receives input from both motor cortices), so a unilateral UMN lesion preserves forehead movement while paralyzing the lower face contralaterally. In LMN lesions (Bell's palsy, parotid tumour, trauma), all ipsilateral facial muscles including the forehead are involved because both cortical inputs converge on the same lower motor neuron.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.