P24-S Abnormal patterns of corticomuscular and intermuscular coherence in acquired and idiopathic/genetic childhood dystonias

Abstract

Background Sensorimotor processing is abnormal in Idiopathic/Genetic dystonias but remains unstudied in Acquired dystonias. We test the hypothesis that sensory modulation of Beta-Corticomuscular coherence (CMC) and Intermuscular coherence (IMC) differs with dystonia aetiology. Methods Participants: 11 children with Acquired dystonia, 5 with Genetic/Idiopathic dystonia and 13 typically-developing-children (TDC) (12–18 yrs). The child grasped a ruler between thumb and index finger. Mechanical perturbations were provided by an electromechanical tapper. Surface EMG (first dorsal interosseous and forearm extensors) and bipolar EEG over contralateral sensorimotor cortex were recorded in 5-s epochs (200×). Signals were amplified, bandpass filtered (EEG 0.5–100 Hz; EMG 5–250 Hz) and digitised (1024 Hz). CMC and IMC were computed using a 512-point short-time Fourier transform and 95% confidence levels were derived. The analysis window moved across the epoch to assess change in CMC/IMC over time. Results Beta-CMC (14–36 Hz) was identified in 13/13 TDCs, 3/5 children with Idiopathic/Genetic and 9/11 with Acquired dystonia. Beta-CMC magnitude increased significantly from baseline to early post-stimulus in TDCs and Acquired dystonia (Wilcoxon signed rank test p = 0.001 and p = 0.004 respectively), but not in Idiopathic/Genetic dystonia (p = 0.959). Post-stimulus beta-CMC magnitude was significantly higher in TDCs than Idiopathic/Genetic dystonia (Mann Whitney p = 0.002) and in Acquired than Idiopathic/Genetic dystonia (p = 0.038). Beta-IMC was similar across groups. Prominent low frequency (4–8 Hz) IMC was seen in all dystonia patients, but not in TDCs, and correlated with severity (BFMDRS-m). Conclusion Idiopathic/Genetic and Acquired dystonia share an abnormal low-frequency IMC but patterns of beta-CMC sensory modulation are distinct, indicating different sensorimotor processing abnormalities between these groups.