Patterns of EMG–EMG coherence in limb dystonia

Abstract

Dystonia of the limbs may be due to a wide range of aetiologies and may cause major functional limitation. We investigated whether the previously described pathological 4 to 7 Hz drive to muscles in cervical dystonia is present in patients with aetiologically different types of dystonia of the upper and lower limbs. To this end, we studied 12 symptomatic and 4 asymptomatic carriers of the DYT1 gene, 6 patients with symptomatic dystonia due to focal basal ganglia lesions, and 11 patients with fixed dystonia, a condition assumed to be mostly psychogenic in aetiology. We evaluated EMG-EMG coherence in the tibialis anterior (TA) of these and 15 healthy control subjects. Ten of 12 (83%) of symptomatic DYT1 patients had an excessive 4 to 7 Hz common drive to TA, evident as an inflated coherence in this band. This drive also involved the gastrocnemius, leading to co-contracting electromyographic bursts. In contrast, asymptomatic DYT1 carriers, patients with symptomatic dystonia, patients with fixed dystonia, and healthy subjects showed no evidence of such a drive or any other distinguishing electrophysiological feature. Moreover, the pathological 4 to 7 Hz drive in symptomatic DYT1 patients was much less common in the upper limb, where it was only present in 2 of 6 (33%) patients with clinical involvement of the arms. We conclude that the nature of the abnormal drive to dystonic muscles may vary according to the muscles under consideration and, particularly, with aetiology.

Psychogenic movement disorders

“…Grosse et al [23 ] reported that this pathological drive was also found in the lower limbs of 10 out of 12 symptomatic patients with DYT1 dystonia, but was seen neither in patients with fixed dystonia (thought to be psychogenic), nor in normal controls. It was also not found in symptomatic dystonia due to focal basal ganglia lesions and asymptomatic carriers of the DYT1 gene.…”

Localization of Basal Ganglia and Thalamic Damage in Dyskinetic Cerebral Palsy

“…Direct quantification of dystonia and spasticity using electromyographic correlates (which may be particularly useful in animal models of hypoxic-ischemic encephalopathy) [52][53][54] 5. Animal studies to test whether lesions in distinct lentiform nuclei differentially induce dystoniform GPi theta and alpha oscillatory activity or dystonic motor phenotypes Focus on implications for treatment 1.…”

Coherence and Phase Locking Disruption in Electromyograms of Patients with Amyotrophic Lateral Sclerosis

“…Rectified y and x are assumed to be realizations of stationary mean time series. Using discrete Fourier transforms, in frequency domain auto spectra f x,x (λ), f y,y (λ) and cross spectrum f x,y (λ) are calculated to assess measures of correlation [9,28]. As a function of frequency, coherence |R x,y (λ)| 2 is assessed by the squared magnitude of the normalized cross spectrum, divided by the product of the two auto spectra as show in equation 2.1.…”

“…Thus, coherence provides a measurable quantity of the fraction of the activity in one sEMG signal that can be foreseen by the activity of the other sEMG signal [28,9]. Hence, coherence quantifies the intensity and range of frequencies where rhythmic synaptic inputs are common across the motoneuron pool [16].…”

“…Coherence is performed using discrete Fourier transforms, so the parameter nonequispaced fast Fourier transform (NFFT), that represents the number of data points used in each block must be defined. For the rectified x and y signals, auto spectra f x,x (λ), f y,y (λ) and cross spectra f x,y (λ) are calculated to assess measures of correlation Grosse et al, 2004). As a function of frequency, cross-correlation is assessed by coherence function -|R x,y (λ)| 2 -defined as the squared magnitude of cross spectrum, normalized by the product of the two auto spectra as show in equation 1.…”