Levodopa effect on electromyographic activation patterns of tibialis anterior muscle during walking in Parkinson’s disease

Previous studies have reported that patients with Parkinson’s disease (PD) show, in the ‘‘off medication’’state, a reduced activation of tibialis anterior (TA) in the late swing–early stance phase of the gait cycle. InPD patients the pathophysiological picture may cause differences among the stride cycles. Our aims wereto evaluate how frequently TA activity is reduced in the late swing–early stance phase and if there is arelationship between the TA pattern and the clinical picture.Thirty PD patients were studied 2 h after Levodopa administration (‘‘on-med’’) and 12 h afterLevodopa wash-out (‘‘off-med’’). They were evaluated by the Unified Parkinson’s Disease Rating Scale(UPDRS III) and surface electromyography of TA and gastrocnemius medialis (GM). The root mean square(RMS) of the TA activity in late swing–early stance phase (RMS-A) was normalized as a percent of theRMS of the TA activity in late stance–early swing (RMS-B).RMS-A was reduced in 30% of patients in the ‘‘off-med’’ condition. Within these patients, thepercentage of stride cycles with reduced RMS-A, ranged between 28% and 83%. After Levodopa intake, nostride cycle showed reduced RMS-A. Patients with reduced RMS-A had a lower UPDRS III total score inthe ‘‘on-med’’ rather than in the ‘‘off-med’’ condition (p = 0.02).Our data confirm and extend previous observations indicating that, in ‘‘off-med’’ the function of TA isimpaired in those patients clinicallymore responsive to Levodopa. TA activation is reduced in a relativelyhigh percent of gait cycles in the ‘‘off-med’’ state. Since the variability of TA activation disappears afterLevodopa administration, this phenomenon could be the expression of an abnormal dopaminergic drive.