rTMS induces brief events of muscle atonia in patients with narcolepsy

Abstract

Study Objectives: To investigate the effect of repetitive transcranial magnetic stimulation (rTMS) in patients with narcolepsy. Design: Using rTMS, three patients with narcolepsy and cataplexy were investigated with and without their anticataplectic medication. rTMS of the motor 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 healthy 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 of not taking their usual anticataplectic medication, rTMS of the motorcortex induced an interruption of voluntary EMG activity in the FDI. EMG reduction lasted from 0.6 to 3.5s and was more pronounced in the hand contralateral to the stimulated hemisphere. This result was not observed in these patients when taking their regular medication nor in the normal controls. Stimulation of other cortical areas, as well as stimulation of the peripheral nervous system, did not induce muscle weakness episodes. Conclusions: We postulate that rTMS of the descending voluntary motor pathway triggers muscle atonia similar to cataplexy by indirectly activating the mechanisms responsible for the generation of muscle atonia during REM sleep and cataplexy. We conclude that rTMS, in the future, might prove to be a useful addition to the diagnostic repertoire for narcolepsy.