Suppression of Motor Evoked Potential and H-reflex during Cataplexy in Narcolepsy

Han, Sun Jung; Joo, Eun Yeon; Kim, Sun Hwa; Jung, So-Hee; Hong, Seung Bong

doi:2007.4.2.48

J Korean Sleep Res Soc > Volume 4(2); 2007 > Article

ORIGINAL ARTICLE

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

한선정, 주은연, 김선화, 정소희, 홍승봉

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

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