Suppression of Motor Evoked Potential and H-reflex during Cataplexy in Narcolepsy |
한선정, 주은연, 김선화, 정소희, 홍승봉 |
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Suppression of Motor Evoked Potential and H-reflex during Cataplexy in Narcolepsy |
Sun Jung Han, Eun Yeon Joo, Sun Hwa Kim, So-Hee Jung, 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: November 25, 2007 Accepted: December 27, 2007 Published online: December 31, 2007 |
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ABSTRACT |
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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