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Defining morphology of periodic leg movements in sleep: an evidence-based definition of a minimum window of sustained activity

  • Neurology • Original Article
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Abstract

Objective

Current standard guidelines for scoring periodic leg movements (PLM) define the start and end of a movement but fail to explicitly specify the movement morphology necessary to classify an EMG event as a PLM, rather than some other muscle event. This is currently left to the expert visual scorer to determine. This study aimed to define this morphology to provide a consistent standard for visual scoring and to improve automatic periodic leg movements in sleep scoring.

Methods

A review of expert PLM scoring produced a hypothesized morphology criterion: a window of high EMG activity within the movement lasting at least 0.5 s. Two diverse expert visual scorers were independently presented with images of EMG tracings from candidate leg movements (CLM) that either passed or failed this requirement (aka “full” or “empty” movements, respectively), and indicated whether each should be scored as CLM. The 0.5-s window was compared with alternatives of 0.25 and 0.75 windows.

Results

Expert scorers on average identified 94 % of “full” movements as CLM in contrast to only 8.5 % of “empty” movements. The proposed minimum window of 0.5 s also resulted in the highest agreement between visual scorers and between scorers and an automatic program.

Conclusion

An added criterion requiring 0.5 s of high EMG activity within a valid CLM improves the accuracy of automatic scoring algorithms in relation to the gold standard of expert visual scorers. Our results suggest that this rule is an accurate representation of the morphology feature used by experts. This new rule has the potential to improve consistency and accuracy of visual and automatic scoring of PLM.

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Acknowledgments

Sleep data acquisition and scoring were provided by The Center for Interdisciplinary Sleep Research and Education (CISRE) at Johns Hopkins University.

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Authors and Affiliations

  1. Center for Restless Legs Study, Department of Neurology, Johns Hopkins University, Baltimore, MD, USA

    Patrick Skeba, Kasidet Hiranniramol, Christopher J Earley & Richard P Allen

  2. Sleep and Epilepsy Center, Neurocenter of Southern Switzerland, Civic Hospital (EOC) of Lugano, Lugano, Switzerland

    Stephany Fulda

Authors
  1. Patrick Skeba
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  2. Stephany Fulda
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  3. Kasidet Hiranniramol
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  4. Christopher J Earley
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  5. Richard P Allen
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Corresponding author

Correspondence to Patrick Skeba.

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Funding

This study was supported in part by a grant from the National Institute for Neurological Diseases and Stroke number NS075184. The sponsor had no role in the design or conduct of this research.

Conflict of interest

All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.

Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Electronic supplementary material

Supplementary Figure 1

The region in red represents an LM as scored by strict WASM standards: it rises above the low threshold (roughly 7 microvolts if one zooms close enough into the picture) and does not remain below that threshold for 0.5 s until the end of the red region. The event is roughly 0.8 s long. Neither of our expert scorers would consider such a short spike (< 0.2 s), followed by such low (but high enough) activity as a legitimate LM, based on their experience. This movement fails our proposed morphology test, using the median window of 0.5 s, but a similar test using the mean accepts this movement. In general, the mean is too affected by extreme values, to exclude short bursts of extremely high energy (which could be anything from fragmentary myoclonus to EKG interference) unrelated to LM. (JPEG 24 kb)

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Skeba, P., Fulda, S., Hiranniramol, K. et al. Defining morphology of periodic leg movements in sleep: an evidence-based definition of a minimum window of sustained activity. Sleep Breath 20, 1293–1299 (2016). https://doi.org/10.1007/s11325-016-1404-2

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  • DOI: https://doi.org/10.1007/s11325-016-1404-2

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