Normal cortical excitability in Myoclonus-Dystonia — A TMS study

ObjectiveThe aim of the present study is to investigate cortical excitability in patients with DYT 11 positive Myoclonus-Dystonia (M-D), using transcranial magnetic stimulation (TMS).MethodsSilent period, motor evoked potential (MEP) recruitment curve, short interval intracortical inhibition (SICI), intracortical facilitation (ICF) and short interval intracortical facilitation (SICF), with short interstimulus intervals (ISIs) ranging from 1.2 to 3.2 ms, were studied in 15 DYT 11-positive M–D patients and their matched controls. In four patients and matched controls peripheral double pulse electrical nerve stimulation was performed.ResultsAll TMS parameters of cortical excitability were normal compared to healthy controls. In the SICF protocol we observed more variable and polyphasic MEPs in M–D patients. Cross-covariance analysis of MEP area revealed a significant correlation difference at ISI 2.2 and 2.8 ms. This increased variability was not seen in other TMS protocols or with peripheral nerve stimulation.ConclusionsIn contrast with other types of dystonia, no changes in cortical excitability were found in DYT 11 patients. Our findings suggest that M–D is both clinically and pathophysiologically a separate entity from other dystonic disorders. Polyphasic MEPs during the SICF protocol in M–D patients could reflect central neuron membrane instability. Application of the SICF protocol in other patient groups has to prove its value in movement disorders.