New research delves into the phenomenology of tremor

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Everything that surrounds us is oscillating. Our physical bodies are no exception. When the amplitude of these oscillations exceeds a certain threshold, it becomes a problem, and we call it tremor. 

Just by performing a physical exam, the clinician should be able to describe the affected body segment, the conditions in which the tremor is present, and also provide a subjective categorization of frequency and amplitude as “low,” “medium,” or “high,” but this assessment may be insufficient. 

By capturing this signal with neurophysiological tools, clinicians can reduce this clinical phenomenon to a time series—a collection of points that represent change over time. This digital representation of the tremor helps determine which muscles are involved, the temporal relationship between agonist and antagonist muscles, and the burst duration. This time series can be further decomposed into sine waves, which are mathematical expressions that closely match the oscillatory activity observed in tremor. Once the tremor is expressed as a collection of sine waves, it becomes possible to assess how rhythmic the clinical phenomenon is and to precisely estimate frequency, amplitude, and phase. Furthermore, one can examine how the frequency changes over time or how the frequencies of different body parts are related. 

By delving into phenomenology, clinicians can differentiate a tremor from rhythmic myoclonus, identify dystonic features, or detect inconsistencies that may suggest a functional cause. Additionally, by observing subtle frequency variations with loading, the coherence between different body segments, and, in some cases, the co-registration of electromyography with electroencephalography signals, it is possible to infer the origin of the tremor. Thus, transitioning from phenomenology to etiology becomes easier. 

Nowadays, there is a strong emphasis on advanced imaging and genetic studies for a precise etiological diagnosis, but these techniques may give confusing results if they are not guided by a thorough phenomenological characterization. Furthermore, in the field of Movement Disorders, most treatments are driven by phenomenology rather than etiology. 

We are convinced that a robust phenomenological characterization is critical for the management of patients with movement disorders, and neurophysiology remains an underutilized tool in this regard. The article entitled “Clinical Neurophysiology for Tremor: Common Questions in Clinical Practice” ¹describes the methodology and interpretation of neurophysiological studies in patients with tremor, with special emphasis on essential tremor, parkinsonism, myoclonus, and functional tremor. It provides an evidence-based background on the different tremor types and discusses neurophysiological approaches based both on evidence and the experience of international experts in the field from the MDS Clinical Neurophysiology Study Group. 

Read the paper »

References

1. Schwingenschuh P, Van Der Stouwe M, Pandey S, et al. Clinical neurophysiology for tremor: Common questions in clinical practice. Parkinsonism Relat Disord. Published online November 2024:107196. doi:10.1016/j.parkreldis.2024.107196 

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