During videonystagmography, a patient shows spontaneous vertical downbeat nystagmus that increases on lateral gaze and does not suppress with visual fixation. This pattern localizes to which anatomical region?

• A Peripheral labyrinth on the right
• B Peripheral labyrinth on the left
• C Vestibular nerve at the cerebellopontine angle
• D Cerebellar flocculus or foramen magnum region ✓

Explanation

Downbeat nystagmus that does not suppress with fixation is a central pattern, most commonly arising from floccular lesions or craniocervical junction pathology such as Chiari malformation. Peripheral lesions produce horizontal nystagmus suppressed by fixation. Options A and B are peripheral patterns. Option C would not typically produce pure vertical nystagmus.

Reference: Neuro-ophthalmology: Diagnosis and Management, 2nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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