Frequency analysis of lower extremity electromyography signals for the quantitative diagnosis of dystonia

The purpose of this study was to develop an objective, quantitative tool for the diagnosis of lower extremity dystonia. Frequency domain analysis was performed on surface and fine-wire electromyography (EMG) signals collected from the lower extremity musculature of ten patients with suspected dystonia while performing walking trials at self-selected speeds. The median power frequency (MdPF) and percentage of total power contained in the low frequency range (%AUCTotal) were determined for each muscle studied. Muscles exhibiting clinical signs of dystonia were found to have a shift of the MdPF to lower frequencies and a simultaneous increase in the %AUCTotal. A threshold frequency of 70 Hz identified dystonic muscles with 73% sensitivity and 63% specificity. These results indicate that frequency analysis can accurately distinguish dystonic from non-dystonic muscles.