Downbeat Nystagmus – Craniocervical Junction — SCE Neurology MCQ

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ModerateNeuro-ophthalmologyDownbeat Nystagmus – Craniocervical JunctionSCE Neurology

A 50-year-old woman with known MS develops nystagmus. Examination shows downbeat nystagmus that worsens on lateral and downward gaze. What pathology does downbeat nystagmus localise to?

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Correct answer: B — The craniocervical junction — particularly lesions at the foramen magnum region (Chiari malformation, MS plaques, meningiomas, or other structural lesions affecting the cervicomedullary junction)

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

Downbeat nystagmus (DBN) localises to the craniocervical junction/lower brainstem, specifically structures around the foramen magnum. The mechanism involves disruption of vertical gaze-holding pathways (flocculus and paraflocculus of the cerebellum, which normally inhibit the anterior semicircular canal pathways). Causes: Chiari malformation (most common structural cause), MS (brainstem plaques), craniocervical tumours, spinocerebellar degeneration, and medications (lithium, carbamazepine, phenytoin). A: Peripheral vestibular lesions cause horizontal/rotatory nystagmus, not downbeat. C/D/E: Cortical lesions do not cause downbeat nystagmus.

Reference: ABN Neuro-ophthalmology Guidelines