Abstract
Transducers are defined as any sensor that converts a physiological signal of tremor into an electrical signal. Evolving technologies have utilized transducers to develop devices for tremor measurement that are more convenient, accurate, and capable of continuous recording. Transducer‐based methods provide valuable diagnostic tools for the clinician that can distinguish between different tremor syndromes and differentiate tremor from other hyperkinetic movement disorders. Transducers are also used to objectively quantify and track tremor symptom severity over time and assess clinical response to intervention (e.g., pharmaceutical treatments or DBS). This video highlights the utility of transducer‐based methods in characterizing and quantifying tremor and reviews the available technologies for measuring tremor. We provide case examples that demonstrate how different technology‐based measures for tremor direct the approach to diagnosis and management of symptoms.
Keywords: tremor, transducer, technology
Video 1. This video shows electromyography (top two rows) and accelerometry (bottom two rows: left hand is second from the bottom; right hand is on the bottom) recording of a woman with both essential tremor and functional tremor. The accelerometer on the right hand exhibits variable amplitude of the postural tremor, which abruptly diminishes after the subject is asked to tap to an externally cued 3‐Hz rhythm with the left hand. After the metronome stops and the subject's left hand goes back to rest, the postural tremor on the right hand reappears. This distractibility is characteristic of functional tremor. (6:27‐7:20)
Video 2. This video shows electromyography recording of bilateral tibialis anterior muscles demonstrating a rhythmical, synchronous, 18‐Hz muscle bursting pattern during standing, consistent with orthostatic tremor. (10:20‐10:43)
Video 3. This video demonstrates digital acquisition of Archimedes spirals for tremor analysis. (11:57‐12:27)
Video 4A. This video demonstrates use of a smartphone app to measure postural tremor with the forearm supported in a man with essential tremor. Frequency analysis measured by the app in the right lower corner shows a 5‐Hz tremor. (14:35‐14:43)
Video 4B. This video demonstrates use of a smartphone app to measure postural tremor in the wing‐beating position in a man with essential tremor. Frequency analysis measured by the app in the right lower corner shows a stable 5‐Hz tremor. (14:44‐14:54)
Video 4C. This video demonstrates use of a smartphone app to measure postural tremor with the forearm supported, with a 1‐kg weight added to the upper limb in a man with essential tremor. Frequency analysis measured by the app in the right lower corner shows an unchanged 5‐Hz tremor, which is consistent with a centrally generated tremor. (14:55‐15:22)
Author Roles
(1) Manuscript: A. Writing of the First Draft, B. Review and Critique; (2) Other: A. Writing of the Video Script, B. Recorded the Video, C. Edited the Video, D. Performed the Electrophysiological Studies, E. Conception of the Article, F. Supervised the Project, G. Revised the Video Content.
K.L.: 2A, 2B, 2C
F.V.‐U.: 2A, 2B, 2D
F.B.N.: 1B, 2E
M.H.: 1B, 2E
D.H.: 1B, 2F, 2G
Disclosures
Ethical Compliance Statement
Patients who were videotaped for this article participated in research protocols approved by the NIH Combined Neurosciences IRB or the UCSD IRB, and provided written informed consent for the respective protocols as well as additional informed consent for videotaping following institutional requirements. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines.
Funding Sources and Conflicts of Interest
This study was supported by the NINDS Intramural Research Program. Dr. Nahab reports a consultancy with Global Kinetics PTY.
Financial Disclosures for previous 12 months
Dr. Katherine Longardner received honoraria from the Lundbeck Neurogenic Orthostatic Hypotension Fellows Advisory Board (Aug. 2018, Aspen, CO). Dr. Felipe Vial Undurraga received salary support through a research project funded by Cala Health Inc. Dr. Fatta Nahab received honoraria from Auspex Pharmaceuticals. Dr. Hallett may accrue revenue on US Patent #6,780,413 B2 (Issued: August 24, 2004): Immunotoxin (MAB‐Ricin) for the treatment of focal movement disorders, and US Patent #7,407,478 (Issued: August 5, 2008): Coil for Magnetic Stimulation and methods for using the same (H‐coil); in relation to the latter, he has received license fee payments from the NIH (from Brainsway) for licensing of this patent. He is on the medical advisory boards of CALA Health, Brainsway, and Cadent. He is on the editorial boards of approximately 15 journals and receives royalties and/or honoraria from publishing from Cambridge University Press, Oxford University Press, Springer, and Elsevier. Dr. Hallett's research at the NIH is largely supported by the NIH Intramural Program. Supplemental research funds have been granted by Allergan for studies of methods to inject botulinum toxins, Medtronic, Inc. for a study of DBS for dystonia, and CALA Health for studies of a device to suppress tremor.
Dr. Dietrich Haubenberger is Special Volunteer at the National Institutes of Neurological Disorders and Stroke, under which capacity the manuscript for this article was developed. Since January 2019, Dr. Haubenberger is an employee of Neurocrine Biosciences, Inc.
Acknowledgments
We thank Scott McAvoy, Digital Media Lab Manager at UC San Diego, for digital media production. We thank Dr. Irene Litvan, Director of the UC San Diego Parkinson and other Movement Disorders Center.
Relevant disclosures and conflicts of interest are listed at the end of this article.