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KMID : 1002120070040020048
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Journal of Korean Sleep Research Society
2007 Volume.4 No. 2 p.48 ~ p.53
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Suppression of Motor Evoked Potential and H-reflex during Cataplexy in Narcolepsy
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Han Sun-Jung
Joo Eun-Yeon
Kim Sun-Hwa
Jung So-Hee
Hong Seung-Bong
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Abstract
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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.
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KEYWORD
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Narcolepsy, Cataplexy, Transcranial magnetic stimulation, Motor evoked potential, H-reflex
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