Re-emergent tremor provocation

Rest and re-emergent tremor (RET) in Parkinson's disease (PD) are known to be markedly variable. The aim of this study is to evaluate the effect of tremor provocation on RET latency and variability.

We performed a prospective observational study in 21 PD patients with RET. Evaluations were conducted by accelerometric analysis of hand movements with and without provocation by counting out loud backwards from 100, in the OFF state. Differences in RET pause duration, tremor power at peak frequency, root mean square (RMS) and slope of return of the tremor after the pause was measured. Inter- and intra-subject variability were also calculated.

RET pause duration showed a 75% decrease after provocation (p < 0.001), which led to zero in 52% of cases, as compared to 9% in unprovoked measurements (p < 0.001). Provocation also led to a 2.57 time increase in tremor power (p < 0.001), 1.37 time increase in RMS (p < 0.001) and 2.47 time increase in slope (p < 0.001). A significant decrease in inter-subject variability was also observed (p = 0.001).

Tremor provocation led to RET amplitude increase, pause shortening, and variability decrease. Therefore, while provocation can be recommended for the evaluation of rest tremor in clinical practice, it might well annul its value for identifying the pause prior to re-emergent tremor.