Objective: To develop ambulatory assessment of tremor in Parkinson’s disease (PD) throughout the day, in relationship to treatment and fluctuations in bradykinesia.

Background: PD is characterised by resting tremor, but postural and kinetic tremors alsooccur. Mostly tremor can be characterised in the consulting room but its relationship to treatment and fluctuations can be clinically helpful especially as patients may confuse dyskinesia with tremor.

Methods: The Parkinson KinetiGraph (PKG, from Global Kinetics) logger contains a triaxial accelerometer and a system for assessing bradykinesia and dyskinesia over a 6 days. The accelerometry data from 6 days of continuous PKG recording was sampled at 50Hz and processed through a 250 sample sliding window in 1s steps. Tremor was identified when in at least 10 consecutive seconds the peak spectral power was 6dB larger than the median between 1-10Hz, was between 2.8Hz and 10Hz and differed by no more than 0.4Hz/s from the frequency of the spectral peak in the two immediately adjacent steps. Percent of time that tremor was present (%T) was calculated as the percentage of time between 09:00 and 18:00 where tremor was identified, having excluded any period that the patient was immobile (asleep).

Results: This algorithm was applied to the PKG of 100 PD subjects who had been assessed clinically for the presence and nature of tremor. For each subject the %T was calculated from the PKG and this was then compared with the clinical presence or absence of tremor. A %T ≥ 0.8 provided a high Sensitivity (92.5%) and Selectivity (92.9%) in identifying tremor. False negatives were mainly low amplitude kinetic or postural tremor which were frequently not apparent to the patient or tremors that did not affect the upper limb. A %T≥1 indicated a high likelihood of the presence of clinical meaningful tremor and a “grey zone” was identified bewteen 0.6 and 1.0 with. This was then retested on a second cohort of 100 patients with a similar outcome. It was also possible in many tremulous patients to use the PKG’s simultaneous bradykinesia scores to find a threshold for the emergence of tremor. Similarly, tremor did not produce false increase in the dyskinesia score in this sample of 200.

Conclusions: This approach to tremor analyses appears to be a useful for assessing the presence of tremor and its relationship to bradykinesia and timing of medications.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/ambulatory-assessment-of-tremor/