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UMN vs LMN Facial Palsy — MFDS Part 1 MCQ

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ModerateHuman DiseaseUMN vs LMN Facial PalsyMFDS Part 1

A patient presents with acute unilateral weakness at the angle of the mouth. Which additional examination finding most strongly favours a unilateral supranuclear upper motor neurone lesion rather than a peripheral lower motor neurone facial nerve lesion?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: E — Preserved forehead wrinkling on the side of the lower facial weakness

Explanation lettering: D = shown as A · E = shown as B · B = shown as D · A = shown as E

A is correct. A unilateral supranuclear corticobulbar lesion classically causes predominantly contralateral lower facial weakness while forehead movement is relatively preserved. This reflects bilateral corticobulbar input to the part of the facial nucleus supplying the upper face. By contrast, a peripheral lower motor neurone lesion of the facial nerve usually weakens both the upper and lower ipsilateral face, so forehead wrinkling is reduced, as in B. Bilateral lower facial weakness suggests a bilateral neurological process rather than the unilateral lesion described. D is not the typical pattern of either lesion, while tongue deviation localises principally to the hypoglossal motor pathway. Forehead sparing is clinically useful but not infallible, so the stem asks which finding most strongly favours the localisation.

Reference: Masterson L, Vallis M, Quinlivan R, Prinsley P. Assessment and management of facial nerve palsy. BMJ. 2015;351:h3725, section “Upper motor neurone”. https://www.bmj.com/bmj/section-pdf/905402?path=/bmj/351/8025/Practice.full.pdf