A 24-year-old woman presented with blurry vision. Examination showed left eye esotropia and slow horizontal saccades bilaterally. Vertical saccade velocity was normal, and there was a “round the houses” sign on diagonal saccades (Video 1). Video head impulse testing (vHIT) reduced gains in the posterior canals bilaterally with relative preservation of anterior and horizontal canal function bilaterally.

Video of Eye Movements. Video shows evidence of left eye esotropia on primary gaze and bilateral slowing of horizontal saccades with normal vertical saccade velocity. Testing of diagonal saccades shows that bilaterally the horizontal component of the movement lags behind the vertical, causing a curved trajectory—the “round the houses” sign.Download Supplementary Video 1 via http://dx.doi.org/10.1212/207968_Video_1

Slowing of the horizontal saccades with sparing of the vertical saccades localizes the lesion to the paramedian pontine reticular formation bilaterally with sparing of the rostral interstitial nucleus of the medial longitudinal fasciculus.1 Reduced gains in both posterior canals on vHIT indicate involvement of the medial longitudinal fasciculus bilaterally,2 findings that are consistent with the imaging, which shows enhancing lesion in the dorsal pons (Figure). CSF tested positive for aquaporin-4 antibodies. The patient was treated with 5 days of plasma exchange, with clinical improvement in the saccades.

FLAIR MRI imaging showing hyperintensity in the dorsal pons evident on coronal (A), axial (B), and sagittal (C) imaging. Video head impulse testing shows reduced gains in the posterior canals bilaterally (D).

U.F. Ashraf: drafting/revision of the manuscript for content, including medical writing for content; study concept or design; analysis or interpretation of data. C. Wang: major role in the acquisition of data; analysis or interpretation of data. G.M. Halmagyi: study concept or design.

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Go to Neurology.org/N for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.

Submitted and editor reviewed. The handling editor was Editor-in-Chief José G. Merino, MD, MPhil, FAHA, FAAN.

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