Premotor-motor excitability is altered in dopa-responsive dystonia

Background: Dopa-responsive dystonia is clinically dominated by a combination of dystonia and parkinsonism, both known to be associated with abnormal activity in premotor-motor circuits. Methods: To probe premotor-motor excitability, we used a transcranial magnetic stimulation dual pulse conditioning paradigm in 15 genetically confirmed dopa-responsive dystonia patients and 20 controls under different medication states. We also determined silent periods, short-latency afferent inhibition, interhemispheric inhibition, and short-interval intracortical inhibition and facilitation. Results: In contrast to healthy controls, no motor cortex inhibition was seen after premotor conditioning regardless of the dopaminergic state in patients. The duration of the ipsilateral silent period was increased in the OFF state, and short-latency afferent inhibition was reduced in the ON compared with the OFF state. Conclusion: Premotor-motor circuits appear hyporesponsive in dopa-responsive dystonia.