Analysis of stimuli triggering attacks of paroxysmal dystonia induced by exertion

In a patient with a familial form of paroxysmal exertion induced dyskinesia (PED), the efficacy of different stimuli and manoeuvres in triggering dyst onic attacks in the arm was studied. As a new approach, transcranial magnet ic stimulation (TMS) of the motor cortex was used to bigger motor paroxysms and to monitor cortical excitability during attacks. Motor paroxysms could be provoked by muscle vibration, passive movements, TMS, magnetic stimulat ion of the brachial plexus, and electrical nerve stimulation. Sham stimulat ion over the motor cortex and thermal and tactile cutaneous stimuli were in effective in triggering attacks. It is concluded that dystonic attacks are triggered by proprioceptive afferents rather than cutaneous stimuli or the descending motor command itself. Outside the attacks, motor cortical excita tory and inhibitory neuronal mechanisms as assessed by TMS (response thresh old and amplitudes, duration of the contralateral and ipsilateral silent pe riod, corticocortical inhibition, and facilitation) were normal, which unde rlines the paroxysmal character of the disorder.