Objective: To conduct a neurophysiological analysis on the postural re-emergence of tremor in PD patients during an acute L-DOPA challenge test.

Background: Some patients with Parkinson’s disease can present postural and action tremor in addition to rest tremor. Previous studies have shown that when patients with rest tremor change position, they commonly have a silent period (SP) without tremor, before its re-emergence. The modification of the re-emergence of Parkinsonian tremor during an acute L-DOPA challenge test has not been previously established.

Methods: An accelerometer-based tremor study was conducted on 6 PD patients with clinically defined re-emergent tremor. The study was performed during an acute L-DOPA challenge test, in order to analyze tremor characteristics in both ON and OFF situations, and to correlate its modifications with the response to the drug. Tremor amplitude and duration of the SP were analyzed in the OFF state (baseline), and every 15 minutes until maximum response to L-DOPA was achieved. Every test was repeated 5 times with and without distraction to ensure consistency.

Results: We observed no time gap between the acquisition of a fixed posture from the resting position and the start of tremor activity displayed by the accelerometer, even when it was not clinically evident. However, tremor amplitude increased, becoming clinically visible after a variable period of time (range 0-22.5 sec). Spectral analysis showed that frequency remained unchanged (5.3±1.0 Hz) with amplitude increment. With distracting maneuvers, the mentioned augmentation came faster, making tremor clinically evident earlier (0.0 sec vs 6.6±7.2 sec, p<0.001), also reducing silent period variability (SP absent). We did observe a dampening of the maximum amplitude of tremor following the administration of L-DOPA (54.5% ± 26.5%), with no change in SP variability nor its mean duration.

Conclusions: Our results suggest that postural SP duration for clinical re-emergence of tremor is highly variable, and can be altered with distraction. It also suggests that it might be an amplitude-related phenomenon, which seems to be clinically rather than electrophysiologically defined. Distraction seems to add up to the amplitude of tremor, making it clinically evident faster. More studies, including patients with mild forms of tremor are needed to confirm this assumptions.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/effect-of-l-dopa-on-re-emergent-tremor-in-parkinsons-disease-a-neurophysiological-assessment/