Using Portable Transducers to Measure Tremor Severity

Background: Portable motion transducers, suitable for measuring tremor, are now available at a reasonable cost. The use of these transducers requires knowledge of their limitations and data analysis. The purpose of this review is to provide a practical overview and example software for using portable motion transducers in the quantification of tremor. Methods: Medline was searched via PubMed.gov in December 2015 using the Boolean expression “tremor AND (accelerometer OR accelerometry OR gyroscope OR inertial measurement unit OR digitizing tablet OR transducer).” Abstracts of 419 papers dating back to 1964 were reviewed for relevant portable transducers and methods of tremor analysis, and 105 papers written in English were reviewed in detail. Results: Accelerometers, gyroscopes, and digitizing tablets are used most commonly, but few are sold for the purpose of measuring tremor. Consequently, most software for tremor analysis is developed by the user. Wearable transducers are capable of recording tremor continuously, in the absence of a clinician. Tremor amplitude, frequency, and occurrence (percentage of time with tremor) can be computed. Tremor amplitude and occurrence correlate strongly with clinical ratings of tremor severity. Discussion: Transducers provide measurements of tremor amplitude that are objective, precise, and valid, but the precision and accuracy of transducers are mitigated by natural variability in tremor amplitude. This variability is so great that the minimum detectable change in amplitude, exceeding random variability, is comparable for scales and transducers. Research is needed to determine the feasibility of detecting smaller change using averaged data from continuous long-term recordings with wearable transducers

Slow Orthostatic Tremor and the Case for Routine Electrophysiological Evaluation of All Tremors

In this issue of the journal, Hassan and Caviness reviewed the controversial topic of slow orthostatic tremor (OT). Based on their review of the relevant literature, Hassan and Caviness concluded that “multiple lines of evidence separate slow OT from classical OT,” but they also noted that “clinical and electrophysiologic overlap may occur.” We were invited to discuss the significance of this overlap within the context of tremor classification

The clinical and electrophysiological investigation of tremor

The various forms of tremor are now classified in two axes: clinical characteristics (axis 1) and etiology (axis 2). Electrophysiology is an extension of the clinical exam. Electrophysiologic tests are diagnostic of physiologic tremor, primary orthostatic tremor, and functional tremor, but they are valuable in the clinical characterization of all forms of tremor. Electrophysiology will likely play an increasing role in axis 1 tremor classification because many features of tremor are not reliably assessed by clinical examination alone. In particular, electrophysiology may be needed to distinguish tremor from tremor mimics, assess tremor frequency, assess tremor rhythmicity or regularity, distinguish mechanical-reflex oscillation from central neurogenic oscillation, determine if tremors in different body parts, muscles, or brain regions are strongly correlated, document tremor suppression or entrainment by voluntary movements of contralateral body parts, and document the effects of voluntary movement on rest tremor. In addition, electrophysiologic brain mapping has been crucial in our understanding of tremor pathophysiology. The electrophysiologic methods of tremor analysis are reviewed in the context of physiologic tremor and pathologic tremors, with a focus on clinical characterization and pathophysiology. Electrophysiology is instrumental in elucidating tremor mechanisms, and the pathophysiology of the different forms of tremor is summarized in this review

Torpedoes in Parkinson's disease, Alzheimer's disease, essential tremor, and control brains

Purkinje cell axonal swellings ("torpedoes"), described in several cerebellar disorders as well as essential tremor (ET), have not been quantified in common neurodegenerative conditions

Estimating Change in Tremor Amplitude Using Clinical Ratings: Recommendations for Clinical Trials

Tremor rating scales are the standard method for assessing tremor severity and clinical change due to treatment or disease progression. However, ratings and their changes are difficult to interpret without knowing the relationship between ratings and tremor amplitude (displacement or angular rotation), and the computation of percentage change in ratings relative to baseline is misleading because of the ordinal nature of these scales. For example, a reduction in tremor from rating 2 to rating 1 (0–4 scale) should not be interpreted as a 50% reduction in tremor amplitude, nor should a reduction in rating 4 to rating 3 be interpreted as a 25% reduction in tremor. Studies from several laboratories have found a logarithmic relationship between tremor ratings R and tremor amplitude T, measured with a motion transducer: logT  =  α·R + β, where α ≈ 0.5, β ≈ –2, and log is base 10. This relationship is consistent with the Weber–Fechner law of psychophysics, and from this equation, the fractional change in tremor amplitude for a given change in clinical ratings is derived: (Tf−Ti)/Ti=10α(Rf−(Ri)−1, where the subscripts i and f refer to the initial and final values. For a 0–4 scale and α  =  0.5, a 1‐point reduction in tremor ratings is roughly a 68% reduction in tremor amplitude, regardless of the baseline tremor rating (e.g., 2 or 4). Similarly, a 2‐point reduction is roughly a 90% reduction in tremor amplitude. These Weber–Fechner equations should be used in clinical trials for computing and interpreting change in tremor, assessed with clinical ratings

Corrigendum: Digitizing Tablet and Fahn–Tolosa–Marín Ratings of Archimedes Spirals have Comparable Minimum Detectable Change in Essential Tremor

Corrigendum to: Elble RJ, Ellenbogen A. Digitizing tablet and Fahn–Tolosan–Marín ratings of Archimedes spirals have comparable minimum detectable change in essential tremor. Tremor Other Hyperkinet Mov. 2017; 7. doi: 10.7916/D89S20H

Digitizing Tablet and Fahn–Tolosa–Marín Ratings of Archimedes Spirals have Comparable Minimum Detectable Change in Essential Tremor

Background:&nbsp;Drawing Archimedes spirals is a popular and valid method of assessing action tremor in the upper limbs. We performed the first blinded comparison of Fahn&ndash;Tolosa&ndash;Mar&iacute;n (FTM) ratings and tablet measures of essential tremor to determine if a digitizing tablet is better than 0&ndash;4 ratings in detecting changes in essential tremor that exceed random variability in tremor amplitude.Methods:&nbsp;The large and small spirals of FTM were drawn with each hand on two consecutive days by 14 men and four women (age 60&plusmn;8.7 years [mean&plusmn;SD]) with mild to severe essential tremor. The drawings were simultaneously digitized with a digitizing tablet. Tremor in each digitized drawing was computed with spectral analysis in an independent laboratory, blinded to the clinical ratings. The mean peak-to-peak tremor displacement (cm) in the four spirals and mean FTM ratings were compared statistically.Results:&nbsp;Test&ndash;retest intraclass correlations (ICCs) (two-way random single measures, absolute agreement) were excellent for the FTM ratings (ICC 0.90, 95% CI 0.76&ndash;0.96) and tablet (ICC 0.97, 95% CI 0.91&ndash;0.99). Log10&nbsp;tremor amplitude (T) and FTM were strongly correlated (logT&nbsp;=&nbsp;&alpha;FTM +&nbsp;&beta;,&nbsp;&alpha;&asymp;0.6,&nbsp;&beta;&asymp;&ndash;1.27, r = 0.94). The minimum detectable change for the tablet and FTM were 51% and 67% of the initial assessment.Discussion:&nbsp;Digitizing tablets are much more precise than clinical ratings, but this advantage is mitigated by the natural variability in tremor. Nevertheless, the digitizing tablet is a robust method of quantifying tremor that can be used in lieu of or in combination with clinical ratings.</p