Bilateral INO – MLF Lesions in MS — SCE Neurology MCQ

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ModerateMultiple Sclerosis & CNS InflammationBilateral INO – MLF Lesions in MSSCE Neurology

A 40-year-old woman with known MS develops acute bilateral internuclear ophthalmoplegia (bilateral INO). What lesion location is most likely?

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Correct answer: B — Bilateral medial longitudinal fasciculi in the brainstem

Bilateral INO results from bilateral MLF lesions in the brainstem (usually pons/midbrain). MS is the most common cause of bilateral INO (in contrast to unilateral INO where stroke is more common). Features: bilateral adduction failure with abducting nystagmus of the contralateral eye on attempted lateral gaze in each direction, with preserved convergence (confirming the oculomotor nuclei/nerves are intact). Bilateral INO in a young person is highly suggestive of MS ('WEBINO' — wall-eyed bilateral INO — is the extreme form with bilateral exotropia). A: Optic nerves cause visual loss, not INO. C: Lateral rectus muscles cause abduction failure. D: Abducens nuclei cause conjugate gaze palsy. E: Oculomotor nuclei cause outward deviation with ptosis.

Reference: NICE NG100 MS; Clinical Neuroanatomy