Rhythmic cortical and muscle discharges induced by fatigue in corticobasaldegeneration

We describe a patient presenting clinical features of corticobasal degenera tion (CBD), including reflex myoclonus in the left upper limb. This patient complained of a marked worsening of involuntary movements in the left uppe r limb after exercise. We analysed the electrophysiological characteristics of myoclonus in the basal state and after a fatiguing exercise in the left upper limb. In the basal condition, single trials recording EEG showed a c ortical complex occurring 20 ms after stimulation of the left median nerve. Surface EMG recordings of the left first dorsal interosseous (FDI) reveale d an isolated biphasic C1 response 49 ms after stimulation. After exercise, single trials recording EEG following shocks to the left median nerve show ed rhythmic complexes with a duration of approximately 80 ms. EEG complexes were made of a series of 3 bursts, with intervals between bursts tending t o cluster at similar to 22 ms. These rhythmic complexes were associated wit h repetitive activity in the left FDI. We conclude that rhythmic cortical a nd muscle discharges can be induced by fatigue in CBD. (C) 2000 Elsevier Sc ience Ireland Ltd. All rights reserved.