Rhythmic cortical and muscle discharges induced by fatigue in corticobasal degeneration

We describe a patient presenting clinical features of corticobasal degeneration (CBD), including reflex myoclonus in the left upper limb. This patient complained of a marked worsening of involuntary movements in the left upper 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 cortical complex occurring 20 ms after stimulation of the left median nerve. Surface EMG recordings of the left first dorsal interosseous (FDI) revealed an isolated biphasic C1 response 49 ms after stimulation. After exercise, single trials recording EEG following shocks to the left median nerve showed rhythmic complexes with a duration of approximately 80 ms. EEG complexes were made of a series of 3 bursts, with intervals between bursts tending to cluster at approximately 22 ms. These rhythmic complexes were associated with repetitive activity in the left FDI. We conclude that rhythmic cortical and muscle discharges can be induced by fatigue in CBD.