[Cerebellar imitation synkineses]

Two patients with autosomal dominant pure cortical cerebellar atrophy, belonging to the same family, exhibited imitation synkineses of hands and feet when the contralateral extremity was moved. The phenomenon was observed particularly when alternate movements of one hand were performed, but it also existed when flexion-extension movements of one foot took place. The induced synkinetic movements were mainly observed on the right side in one patient and exclusively observed on the right side in the other one. At electromyography, the imitation synkinesis took place about 200 milliseconds after the first inducing movement, but tended to be simultaneous with the following ones. Imitation synkinesis appeared to be shared by other cerebellar conditions: 8 cases of sporadic pure cerebellar atrophy and 2 cases of post-surgical injury of the anterior lobe vermis. In the 2 genetic cases, there was no pyramidal sign nor sensitive disturbance, the somesthesic evoked potentials being normal. Thus, the imitation synkinesis was considered as having a cerebellar origin. The cerebellar imitation synkinesis might be provoked by the lack of a physiologic cerebellar inhibition located in the paleo- and/or neo-cerebellum. The predominance of imitation synkineses on the right side suggests that cerebellar inhibition is stronger for the dominant side, in order to liberate it from archaic synkineses.