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J Korean Sleep Res Soc. 2007;4(2):48-53.         doi: https://doi.org/10.13078/jksrs.07009
Suppression of Motor Evoked Potential and H-reflex during Cataplexy in Narcolepsy
Sun Jung Han, Eun Yeon Joo, Sun Hwa Kim, So-Hee Jung, and Seung Bong Hong
1Department of Neurology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
2Department of Neurology, Sanbon Medical Center, College of Medicine, Wonkwang University, Gyeonggi-do, Korea
3Clinical Trial Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
Corresponding Author: Seung Bong Hong ,Tel: +82-2-3410-3592, Fax: +82-2-3410-0052, Email: sbhong@skku.edu / seungbong.hong@samsung.com
Received: 25 November 2007;  Accepted: 27 December 2007.
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Objectives: To investigate the electrophysiologic mechanism of cataplexy, the authors measured motor evoked potential (MEP) and H-reflex during asymptomatic, cataplectic and post-cataplectic periods in a narcolepsy patient.
Methods: For MEP recording, transcranial magnetic stimulation (TMS) was applied to the right and left hemispheres using a Magstim 200 stimulator and a figure of 8-shaped coil. MEP amplitudes in resting state were measured at stimulus intensities of 120 and 150% of resting motor threshold (rMT). H-reflex was elicited by electrical stimuli on a tibial nerve.
Results: rMT at baseline was 43% in the right and 39% in the left hemisphere. Mean MEP amplitude at baseline was 1.15 mV at a stimulation intensity of 120% rMT and 1.77 mV at 150% rMT. During a cataplectic episode, MEP amplitude abruptly decreased to 0.15 mV at 120% rMT and 0.18 mV at 150% rMT when the patient began to feel facial weakness and experience difficulty talking; subsequently no MEP was evoked during loss of whole body muscle tone. H-reflexes were well elicited during asymptomatic periods (mean amplitude: 2.55 mV at 10.0 mA) whereas H-reflex amplitude abruptly decreased and then disappeared after a cataplectic attack started. Conclusion: Suppression of both MEP and H-reflex during cataplexy indicates that postsynaptic spinal motor neuron inhibition is the main pathomechanism underlying cataplexy.
Keywords: Narcolepsy | Cataplexy | Transcranial magnetic stimulation | Motor evoked potential | H-reflex
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