rTMS induces brief events of muscle atonia in patients with narcolepsy

Study Objectives: To investigate the effect of repetitive transcranial magn etic stimulation (rTMS) in patients with narcolepsy. Design: Using rTMS, three patients with narcolepsy and cataplexy were inves tigated with and without their anticataplectic medication. rTMS of the moto r cortex was performed at an intensity of 110% of resting motor threshold, a frequency of 20 Hz, and a duration of 2s. EMG activity was' recorded for both the right and left first dorsal interosseous muscle (FDI). Eight healt hy controls were also investigated under the same conditions. Setting: The study was carried out in the sleep laboratory of the Neurology Department (University of Aachen). Patients: One female and two male patients with narcolepsy/cataplexy. Interventions: N/A Measurements and Results: In three narcoleptic patients, after three days o f not taking their usual anticataplectic medication, rTMS of the motorcorte x induced an interruption of voluntary EMG activity in the FDI. EMG reducti on lasted from 0.6 to 3.5s and was more pronounced in the hand contralatera l to the stimulated hemisphere. This result was not observed in these patie nts when taking their regular medication nor in the normal controls. Stimul ation of other cortical areas, as well as stimulation of the peripheral ner vous system, did not induce muscle weakness episodes. Conclusions: We postulate that rTMS of the descending voluntary motor pathw ay triggers muscle atonia similar to cataplexy by indirectly activating the mechanisms responsible for the generation of muscle atonia during REM slee p and cataplexy. We conclude that rTMS, in the future, might prove to be a useful addition to the diagnostic repertoire for narcolepsy.