A Novel Accelerometry Method to Perioperatively Quantify Essential Tremor Based on Fahn-Tolosa-Marin Criteria

Abstract

The disease status, progression, and treatment effect of essential tremor (ET) patients are currently assessed with clinical scores, such as the Fahn-Tolosa-Marin Clinical Rating Scale for Tremor (FTM). The use of objective and rater-independent monitoring of tremors may improve clinical care for patients with ET. Therefore, the focus of this study is to develop an objective accelerometry-based method to quantify ET, based on FTM criteria. Thirteen patients with ET and thirteen matched healthy participants underwent FTM tests to rate tremor severity, paired with tri-axial accelerometric measurements at the index fingers. Analogue FTM assessments were performed by four independent raters based on video recordings. Quantitative measures were derived from the accelerometric data, e.g., the area under the curve of power in the 4-8 Hz frequency band (AUCP) and maximal tremor amplitude. As such, accelerometric tremor scores were computed, using thresholds based on healthy measurements and FTM criteria. Agreement between accelerometric and clinical FTM scores was analyzed with Cohen's kappa coefficient. It was assessed whether there was a relationship between mean FTM scores and the natural logarithm (ln) of the accelerometric outcome measures using linear regression. The agreement between accelerometric and FTM scores was substantial for resting and intention tremor tests (≥72.7%). However, the agreement between accelerometric postural tremor data and clinical FTM ratings (κ = 0.459) was low, although their logarithmic (ln) relationship was substantial (R² ≥ 0.724). Accelerometric test-retest reliability was good to excellent (ICC ≥ 0.753). This pilot study shows that tremors can be quantified with accelerometry, using healthy thresholds and FTM criteria. The test-retest reliability of the accelerometric tremor scoring algorithm indicates that our low-cost accelerometry-based approach is a promising one. The proposed easy-to-use technology could diminish the rater dependency of FTM scores and enable physicians to monitor ET patients more objectively in clinical, intraoperative, and home settings.

Keywords: Fahn–Tolosa–Marin tremor rating scale; accelerometry; algorithm; essential tremor; quantification.

Figure 1

Accelerometer positioned on the left index finger.

Figure 2

Example PSD periodogram, with the AUCP (4–8 Hz) given in blue.

Figure 3

Flowchart of the accelerometry-based scoring algorithm, based on HP thresholds calculated from healthy participants (HPs) and standardized FTM scoring criteria. Following the flowchart, the “No” pathways are given in blue and the “Yes” pathways are given in orange.

Figure 4

Boxplots of the AUCP between 4 Hz and 8 Hz of the resting (a), postural (c), and intention (e) tremor tests, and of the amplitude of the resting (b), postural (d), and intention (f) tremor tests in the healthy participants and the patient group (per FTM score).

Figure 5

Contingency tables of the mean FTM scores and calculated accelerometry (ACC) scores of the resting (a), postural (b), and intention (c) tremor tests in the patient population.