Assessing tremor severity with long-term tremor recordings

Latency of re-emergent tremor in Parkinson's disease is influenced by levodopa

INTRODUCTION

Re-emergent tremor (RET) is a common form of postural tremor observed in Parkinson's disease (PD) patients. Recent studies have shown that administration of levodopa decreases RET amplitude. However, drug effects on tremor pause duration are less clear.

METHODS

We performed a prospective observational study in PD patients with RET, subjected to acute levodopa challenge. Tremor activity was measured during OFF and ON states both clinically, as well as by using accelerometers taped to the back of both hands. Correlation between RET amplitude and pause duration, as well with MDS-UPDRS scores were investigated. The slope of gradual increase of postural tremor after the pause was also measured in the OFF and ON states.

RESULTS

Significant inverse correlation between tremor amplitude and RET pause duration was observed in OFF (rs = -0.474, p = 0.030) and ON (rs = -0.569, p = 0.006) states. Levodopa reduced tremor amplitude (26%, p = 0.004) dampening slope gradient (22%, p = 0.029). Tremor pause duration also showed inverse correlation with postural tremor amplitude measured by MDS-UPDRS in OFF (rs = -0.311, p = 0.048) and ON (rs = -0.503, p = 0.020) states, as well as with total MDS-UPDRS Part III score (rs = -0.295, p = 0.009). Finally, accelerometric analysis proved to be more sensitive than visual inspection for detecting tremor pauses.

CONCLUSION

Our results suggest RET pause duration is amplitude related, since levodopa-induced amplitude decrease led to pause prolongation, associated with decreased tremor intensity and slope gradient dampening.

Provocation of Parkinsonian tremor

Classical Parkinsonian rest tremor typically fluctuates over time and can be provoked by stressful situations. We quantified and compared the influence of different provocation methods on classical rest tremor severity. The effect of counting backwards from 100, tapping of the contralateral foot and a Stroop test on the Unified Parkinson's Disease Rating Scale (UPDRS) III rest tremor scores and the accelerometrically measured tremor amplitudes (total power) were analyzed in 18 patients with Parkinson's disease and a Type I tremor. Each of the three provocation methods increased the UPDRS III rest tremor score by 1-2 and the total power by 1-2 orders of magnitude compared with baseline (P < 0.001). The maximal effect was reached on average after 2-3 minutes of provocation. The effects were not significantly different. Provocations clearly influence the result of clinical rest tremor ratings, with the kind of provocation being of minor importance. We therefore suggest that each assessment of Parkinsonian rest tremor should include a systematic provocation and this should be formally included in future versions of the UPDRS.

Pramipexole in patients with Parkinson's disease and marked drug resistant tremor: a randomised, double blind, placebo controlled multicentre study

OBJECTIVE

To compare the tremorlytic properties of pramipexole, a non-ergoline dopamine agonist to those of placebo as add on medication in patients with Parkinson's disease.

METHODS

Eighty four patients with early or advanced Parkinson's disease and marked, drug resistant tremor under a stable and optimised antiparkinsonian medication were included in a double blind, randomised, placebo controlled, multicentre study and assigned to add on treatment (7 week dose titration interval, 4 week maintenance period) with either pramipexole (n=44) or placebo (n=40) as adjunct. The primary end point was the absolute change in tremor score, defined as the sum of tremor related items (16, 20, 21) of the unified Parkinson's disease rating scale (UPDRS) in "on" periods. Secondary end points included the percentage change in tremor score, the absolute and percentage changes in long term EMG tremor registration, and the change in tremor self rating scales. Safety and tolerability were assessed on the basis of adverse events, laboratory tests, ECG, and vital signs.

RESULTS

Pramipexole was significantly superior to placebo with a difference between treatment groups in the mean absolute change in tremor score of -4.4 (95% confidence interval (95% CI) -6.2 to -2.5) (p<0.0001), corresponding to a difference in the mean percentage change of -34.7% in favour of pramipexole. The secondary end points were consistent with the significant change in tremor score and provided further evidence for the benefit of pramipexole compared with placebo. Long term EMG registration as an objective measure showed a difference in mean absolute change in tremor occurrence of -15.2% (95%CI -21.4 to -9.0) (p<0.0001), and a difference in the mean percentage change of -45.7% in favour of pramipexole. The treatment effects increased during dose titration and remained stable during the 4 week maintenance dose period until the end of the study. The average daily pramipexole dose during maintenance was 4.1 (SD 0.9) mg. Safety analysis showed an increased rate of fatigue, insomnia, nausea, abdominal pain, and headache under pramipexole, comparable with previous studies.

CONCLUSION

Pramipexole proved to be an effective agent for patients with Parkinson's disease and drug resistant tremor.

Wrist tremor: investigation of agonist-antagonist interaction by means of long-term EMG recording and cross-spectral analysis

We have developed a method to observe and quantify the phasic relationship between the burst patterns of antagonistic muscles in any roughly periodic movement, such as tremor, for up to 24 h. This paper describes our approach, in which long-term EMG recordings are evaluated by a procedure based on cross-spectral analysis. The method is then illustrated by data from 6 patients with essential tremor. Our data confirm earlier observations that a particular patient may show different burst patterns at different times. However, as opposed to tremor analysis based on short-term recording, our method allows quantitative statements on the relative frequency of the burst patterns, as they occur under everyday conditions. In addition, our data suggest that in ET (a) alternating tremor activity in one hand may occur simultaneously with synchronous activity in the other hand; (b) along with the classical alternating and co-contracting patterns there may be significant 'non-classical' activity, that cannot be called alternating or synchronous.

Reliability, specificity and sensitivity of long-term tremor recordings

We have developed a method of long-term EMG recording that has proven suitable for the quantification of pathological tremor. In the present paper we show that the principal parameters of the method (tremor occurrence, tremor intensity, tremor frequency) are highly reproducible and that the method is specific and sensitive for detection of pathological tremor. Twelve patients with essential tremor (ET) and 13 patients with Parkinson's disease (PD) were recorded repeatedly on 3 successive days. For each patient group and for each parameter the intersubject variability was much larger than the intersubject variability. The intraclass correlation coefficient "R" was in the order of 0.9 for each parameter and the mean of Pearson's correlation coefficient between successive days was also approximately 0.9. Recordings from normal controls demonstrated that the method's specificity for pathological tremor is 94.1% and its sensitivity is 96%.

Variations on tremor parameters

This paper describes our analysis procedure for long-term tremor EMG recordings, as well as three examples of applications. The description of the method focuses on how characteristics of the tremor (e.g. frequency, intensity, agonist-antagonist interaction) can be defined and calculated based on surface EMG data. The resulting quantitative characteristics are called "tremor parameters." We discuss sinusoidally modulated, band-limited white noise as a model for pathological tremor-EMG, and show how the basic parameters can be extracted from this class of signals. The method is then applied to (1) estimate tremor severity in clinical studies, (2) quantify agonist-antagonist interaction, and (3) investigate the variations of the tremor parameters using simple methods from time-series analysis. (c) 1995 American Institute of Physics.