Intra- and inter-limb coherency during stance in non-dyskinetic and dyskinetic patients with Parkinson's disease

ObjectiveExamine the level of intra- and inter-limb coherency in non-dyskinetic and dyskinetic patients with Parkinson's disease (PD).Patients & MethodsUsing a magnetic tracking system, whole-body 3D movements were assessed in 10 dyskinetic patients with clear monophasic peak-dose levodopa-induced dyskinesia (LID), in 10 non-dyskinetic patients and in 10 control subjects, standing with their arms out. Patients were tested during their best ON period. Coherency in the kinematics of pairs of body segments was assessed by spectral analysis. For each pair examined, we calculated the highest coherency between 0.5 and 3.0 Hz and the frequency at which this maximum coherency occurred.ResultsAnalysis of variance showed that for 34 out of the 44 (77.3%) comparisons we studied, there were significant differences between the means of coherencies of the groups. Typically, the control group had the highest coherency and the patients with LID had the lowest. Patients with LID also tended to have their maximum coherency at higher frequencies than the control and non-dyskinetic patient groups (30 out of 44 comparisons were significant). These trends appeared in all types of inter-segment comparisons, including bilaterally symmetric segments, biomechanically linked segments (in which coherencies were higher overall in all groups, but still different between groups) and in other comparisons, but the trends were not so clear for comparisons involving the feet.ConclusionLID is indeed incoherent in the frequency domain, suggesting that body segments may be driven by different neural outputs. The challenges of dealing with these incoherent involuntary movements when planning and executing voluntary movements must certainly play a role in motor difficulties observed in patients with LID. The fact that both dyskinetic and non-dyskinetic patients showed less coherency than controls suggests that levodopa may alter postural control by decreasing stiffness and increasing limb independence.