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Skew Deviation vs Trochlear Palsy — SCE Neurology MCQ

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HardNeuro-ophthalmologySkew Deviation vs Trochlear PalsySCE Neurology

A 60-year-old woman presents with acute onset of a skew deviation — her right eye is hypertropic relative to the left. She also has an ipsilateral head tilt to the left. This occurred in the context of a brainstem stroke. What does skew deviation indicate and how is it distinguished from a trochlear nerve palsy?

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Correct answer: C — Skew deviation is a vertical misalignment caused by an imbalance in otolithic (vestibular) inputs from a brainstem/cerebellar lesion — unlike CN IV palsy, the hypertropia in skew deviation does NOT worsen on contralateral head tilt (negative Bielschowsky test), and it is comitant (same in all gaze directions)

Skew deviation is a vertical misalignment of the eyes caused by disruption of otolithic (graviceptive) vestibular pathways, typically from brainstem or cerebellar lesions. It is a CENTRAL sign and is part of the ocular tilt reaction (skew deviation + head tilt + cyclotorsion). Key differences from CN IV palsy: (1) skew deviation is usually comitant (same vertical misalignment in all gaze directions) whereas CN IV palsy is incomitant (worsens in specific gaze directions), (2) Bielschowsky test is negative in skew deviation but positive in CN IV palsy, (3) skew deviation is central (brainstem/cerebellar) whereas CN IV palsy is peripheral. A: They are different entities. C: Skew deviation is a central sign. D: It causes vertical diplopia. E: It indicates a central (brainstem) lesion.

Reference: ABN Neuro-ophthalmology Guidelines; Kattah et al. HINTS Study