Penlight-cover test: a new bedside method to unmask nystagmus
- 1Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- 2Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- 3Krieger School of Arts and Sciences, The Johns Hopkins University, Baltimore, Maryland, USA
- 4Department of Otolaryngology Head and Neck Surgery, The Johns Hopkins Hospital, Baltimore, Maryland, USA
- 5Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- 6Department of Otolaryngology Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- Dr D E Newman-Toker, Department of Neurology, The Johns Hopkins Hospital, Pathology Building 2-210, 600 North Wolfe Street, Baltimore, MD 21287, USA; toker{at}jhu.edu
- Received 31 January 2009
- Revised 9 March 2009
- Accepted 12 March 2009
- Published Online First 30 March 2009
Abstract
Background: Most patients with acute vestibular syndrome have vestibular neuritis or labyrinthitis. Some harbour strokes that can only be differentiated on the basis of subtle eye movement findings, including nystagmus. Peripheral nystagmus should be enhanced by removal of visual fixation. Current bedside methods for removing fixation require expensive equipment or technical skill not routinely available. We sought to test a new method for blocking fixation.
Methods: Proof-of-concept study for a new bedside oculomotor diagnostic test using an established physiological measurement of eye movements (electro-oculography (EOG)) as the reference standard. We sampled unselected patients undergoing caloric testing (surrogate model for neuritis) in an academic vestibular clinic. During the brief (30–60 s) decay phase of caloric-induced peripheral vestibular nystagmus, we shone a penlight in the left eye while intermittently occluding the right. We assessed nystagmus intensity (slow-phase velocity) clinically in all subjects and quantified change in two exemplar cases.
Results: Caloric responses frequently decayed before the test was complete, and artefacts rendered many EOGs uninterpretable during the short decay period. A clinically evident increase in nystagmus was seen 18 times in 10 patients and corroborated by EOG in 15. In quantified cases, slow-phase velocity increased as expected (mean change +42%) with fixation blocked.
Conclusion: The penlight-cover test could offer a low-cost, simple means of disrupting visual fixation in clinical settings where differentiating peripheral from central vestibular disorders is crucial, such as the emergency department. Prospective studies are needed to determine the test’s utility for excluding dangerous central causes among patients with suspected peripheral lesions.
Footnotes
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▸ Additional videos are published online only at http://jnnp.bmj.com/content/vol80/issue8
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Funding: The preparation of this manuscript was supported by grants from the National Institutes of Health (NIH RR17324-01) and the Agency for Healthcare Research and Quality (AHRQ HS017755-01).
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Competing interests: None.
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Ethics approval: Ethics approval was provided by the Johns Hopkins Medicine Institutional Review Board.
