Saccadic intrusions refer to inappropriate saccades that interrupt fixation.1 A 69-year-old woman with progressive supranuclear palsy showed alternating horizontal saccades that intruded on steady fixation (video at Neurology.org). The immediate drift-back of the eyes indicates a saccadic pulse without a step signal (pulse-step mismatch) or return saccade, consistent with single saccadic pulses (SSP).1
The alternating SSP indicates unstable burst neurons for horizontal saccades, which are located in the paramedian pontine reticular formation and are inhibited by the omnipause neurons. Given the prominent atrophy of the midbrain (figure), degeneration of the fixation neurons in the superior colliculus may underlie these involuntary eye movements.2
(A) Video-oculography demonstrates alternating horizontal saccades and immediate drift-back of the eyes after each saccade, which indicates no step signal (pulse-step mismatch) or return saccade (single saccadic pulses). LH = horizontal position of the left eye; LV = vertical position of the left eye; RH = horizontal position of the right eye; RV = vertical position of the right eye. (B) T1-weighted MRIs show a marked atrophy of the midbrain, giving the Mickey Mouse and hummingbird appearances that are typical of progressive supranuclear palsy.
AUTHOR CONTRIBUTIONS
Dr. Lee, as the first author, contributed to analysis and interpretation of the data and drafting of the manuscript. Dr. Choi contributed to interpretation of the data and critical revision of manuscript. Dr. Kim, as the corresponding author, contributed to design of the study, interpretation of the data, and critical revision of the manuscript.
STUDY FUNDING
This study was supported by grants from the Korea Health 21 R&D Project, Ministry of Health & Welfare, Republic of Korea (A080750).
DISCLOSURE
E. Lee and J. Choi report no disclosures relevant to the manuscript. J. Kim serves as an Associate Editor of Frontiers in Neuro-otology and on the editorial boards of the Journal of Korean Society of Clinical Neurophysiology, Research in Vestibular Science, Journal of Clinical Neurology, Frontiers in Neuro-ophthalmology, Journal of Neuro-ophthalmology, and Journal of Vestibular Research. Go to Neurology.org for full disclosures.
ACKNOWLEDGMENT
The authors thank Drs. David S. Zee and Jorge Otero-Millan for comments on the patient.
Footnotes
Go to Neurology.org for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
Supplemental data at Neurology.org
Download teaching slides: Neurology.org
- © 2017 American Academy of Neurology
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