How to do an electrophysiological study of tremor.
Clinical neurophysiology practice
The electrophysiological characterization of hand tremors is a useful method to complement the history and physical exam of tremor patients. Our article describes the methodology (recording, processing and interpretation) used in a diagnostic/phenotypic hand tremor study conducted in our lab at the Human Motor Control Section of the National Institute of Neurological Disorders and Stroke (NINDS), at the National Institutes of Health. The necessary equipment includes two one-axis accelerometers and four-channel electromyography (EMG). The hand tremor is recorded at rest, posture with and without weight loading, and during movement (kinetic). The recorded signals are analyzed in the time and frequency domains. The characterization of the dominant frequencies in the accelerometers and their relationship with the EMG frequencies are essential for the differential diagnosis of different tremor syndromes. We describe the electrophysiological characteristics of several tremor syndromes such as enhanced physiological tremor, essential tremor, Parkinson tremor, pharmacological-induced tremor, orthostatic tremor, and functional (psychogenic) tremor. Simplified guidance for adoption of tremor studies as a clinical tool in a movement disorders subspecialty clinic is provided.
10.1016/j.cnp.2019.06.002
How typical are 'typical' tremor characteristics? Sensitivity and specificity of five tremor phenomena.
van der Stouwe A M M,Elting J W,van der Hoeven J H,van Laar T,Leenders K L,Maurits N M,Tijssen M A J
Parkinsonism & related disorders
INTRODUCTION:Distinguishing between different tremor disorders can be challenging. Some tremor disorders are thought to have typical tremor characteristics: the current study aims to provide sensitivity and specificity for five 'typical' tremor phenomena. METHODS:Retrospectively, we examined 210 tremor patients referred for electrophysiological recordings between January 2008 and January 2014. The final clinical diagnosis was used as the gold standard. The first step was to determine whether patients met neurophysiological criteria for their type of tremor. Once established, we focused on 'typical' characteristics: tremor frequency decrease upon loading (enhanced physiological tremor (EPT)), amplitude increase upon loading, distractibility and entrainment (functional tremor (FT)), and intention tremor (essential tremor (ET)). The prevalence of these phenomena in the 'typical' group was compared to the whole group. RESULTS:Most patients (87%) concurred with all core clinical neurophysiological criteria for their tremor type. We found a frequency decrease upon loading to be a specific (95%), but not a sensitive (42%) test for EPT. Distractibility and entrainment both scored high on sensitivity (92%, 91%) and specificity (94%, 91%) in FT, whereas a tremor amplitude increase was specific (92%), but not sensitive (22%). Intention tremor was a specific finding in ET (85%), but not a sensitive test (45%). Combination of characteristics improved sensitivity. CONCLUSION:In this study, we retrospectively determined sensitivity and specificity for five 'typical' tremor characteristics. Characteristics proved specific, but few were sensitive. These data on tremor phenomenology will help practicing neurologists to improve distinction between different tremor disorders.
10.1016/j.parkreldis.2016.06.008
Spiralometry: computerized assessment of tremor amplitude on the basis of spiral drawing.
Kraus Peter H,Hoffmann Arndt
Movement disorders : official journal of the Movement Disorder Society
Spiral drawing has been used for the assessment of the impact of therapy on motor performance in various movement disorders (e.g. in Parkinson's disease, especially for tremor and hypokinesia). Nevertheless, there are only few guidelines available providing some kind of standardized interpretation. The published protocol with the highest standard is that of Bain and Findley. Kinetic tremor assessed by spiral drawing is not quantified by alternative approaches so far and is not even considered by most rating scales. However, kinetic tremor is quite common and represents a significant impairment in the everyday life of parkinsonian patients. More complex instrumental methods for the quantification of kinetic tremor have not been practical as they, e.g., require relatively expensive equipment or have an unfavourable effort/benefit ratio. We pursued an alternative approach, where we scan drawn spirals to a computer-algorithm that calculates the tremor amplitude. Our standardized method can be applied without difficulty in patients needing only paper and pencil. The evaluation is fully automated, and therefore, it is appropriate for the assessment of therapeutic efficacy in very large populations. The objectivity of the approach represents a significant advantage. In the actual paper, we present how we analyzed the original spirals published by Bain and Findley to validate our computerized assessment. We found a highly significant connection between both methods (explained variance: 88.9%).
10.1002/mds.23193
Estimating Change in Tremor Amplitude Using Clinical Ratings: Recommendations for Clinical Trials.
Elble Rodger J
Tremor and other hyperkinetic movements (New York, N.Y.)
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 and tremor amplitude , measured with a motion transducer: log = α· + 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: (T-T)/T=10-1, where the subscripts and 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.
10.7916/D89C8F3C
Tremor amplitude is logarithmically related to 4- and 5-point tremor rating scales.
Elble Rodger J,Pullman Seth L,Matsumoto Joseph Y,Raethjen Jan,Deuschl Günther,Tintner Ron,
Brain : a journal of neurology
Tremor rating scales (TRSs) are used commonly in the clinical assessment of tremor, but the relationship of a TRS to actual tremor amplitude has never been quantified. Consequently, the resolution of these scales is unknown, and the clinical significance of a 1-point change in TRS is uncertain. We therefore sought to determine the change in tremor amplitude that corresponds to a 1-point change in a typical 5-point TRS. Data from five laboratories were analysed, and 928 patients with various types of hand tremor were studied. Hand tremor was quantified with a graphics tablet in three different labs, an accelerometer in three labs and a mechanical-linkage device in one lab. Tremor in writing, drawing, horizontal posture, rest and finger-nose testing was graded using a variety of TRSs. The relationship between TRS scores and tremor amplitude was computed for each task and laboratory. A logarithmic relationship between a 5-point (0-4) TRS and tremor amplitude (T, measured in centimetres) was found in all five labs, despite widely varying rating scales and transducer methodology. Thus, T2/T1 = 10(alpha(TRS2-TRS1)). The value of alpha ranged from 0.414 to 0.441 for writing, 0.355-0.574 for spiral drawing, 0.441 to 0.488 for rest tremor, 0.266-0.577 for postural tremor and 0.306 for finger-nose testing. For alpha = 0.3, 0.4, 0.5, 0.6 and 0.7, the ratios T2/T1 for a 1-point decrease in TRS are 0.501, 0.398, 0.316, 0.251 and 0.200. Therefore, a 1-point change in TRS represents a substantial change in tremor amplitude. Knowledge of the relationship between TRS and precise measures of tremor is useful in interpreting the clinical significance of changes in TRS produced by disease or therapy.
10.1093/brain/awl190
Habituation and rebound to thalamic deep brain stimulation in long-term management of tremor associated with demyelinating neuropathy.
Patel Neepa,Ondo William,Jimenez-Shahed Joohi
The International journal of neuroscience
Some patients may experience tolerance to chronic ventral intermediate (ViM) thalamic deep brain stimulation (DBS), which may include habituation (loss of sustained tremor control over weeks to days after an adjustment) and rebound (a temporary increase in tremor intensity after stopping DBS). We observed an association between these efficacy limiting phenomena with co-morbid demyelinating sensorimotor peripheral neuropathy (MRT-PN). The clinical and treatment characteristics of neuropathy and tremor pre- and post-DBS are described through retrospective chart review of five patients with MRT-PN. Programming strategies (number of programming visits/implant years and number of major parameter changes/electrode) were compared in MRT-PN patients to a group of seven ET patients without neuropathy, who had > 4 years continuous follow-up. The presence of habituation and rebound were recorded. All MRT-PN patients had initial good response to DBS followed by habituation and/or rebound of tremor control, some asymmetrically. Compared to ET without neuropathy (mean follow-up 5.83 ± 0.78 years), MRT-PN patients (mean follow-up 4.90 ± 3.73 years) required more programming visits/year (p = 0.12) and major parameter changes/electrode/implant year (p = 0.03). The presence of neuropathy may alter tremor characteristics and result in temporary re-setting of thalamic oscillatory drive after DBS in MRT-PN patients. Clinicians should be aware of the risk for tolerance to DBS in MRT-PN and patients should be counseled about possible suboptimal sustained tremor control.
10.3109/00207454.2014.895345
Tremor.
Elias W Jeffrey,Shah Binit B
JAMA
Tremor, defined as a rhythmic and involuntary movement of any body part, is the most prevalent movement disorder, affecting millions of people in the United States. All adults have varying degrees of physiological tremor so it is imperative to distinguish physiological tremor from pathological tremor types. Tremor is not inherently dangerous, but it can cause significant disability at home and in the workplace. Common tremors like essential tremor and Parkinson disease tremor can be recognized by most clinicians at the early stages for the initiation of disease-specific medical therapies. Less common tremors, such as those induced by drugs or brain lesions, are also important to recognize because they may be more refractory to medical therapies and may require earlier referral to a neurological specialist. In patients with the most progressive and severe tremors that are resistant to medical therapies, surgical interventions are available and typically target deep brain regions with stimulation or lesioning. This Grand Rounds review describes the evaluation and evidence-based management of the most common tremors, essential tremor and Parkinson disease tremor.
10.1001/jama.2014.1397
Drug-induced tremors.
Morgan John C,Sethi Kapil D
The Lancet. Neurology
Tremor is a common complaint for many patients. Caffeine and beta-adrenergic agonists are well-recognised drugs that cause or exacerbate tremors. Other tremorogenic drugs, such as selective serotonin reuptake inhibitors and tricyclic antidepressants, are less well recognised. Recognition of the drugs that can cause or exacerbate tremors can help prompt diagnosis, avoids unnecessary tests, and allows clinicians to quickly take corrective action (usually by discontinuing the tremor-inducing drugs). The aim of this review is to provide clinicians with current information on drugs that are associated with tremor and the correct treatment of these drug-induced tremors.
10.1016/S1474-4422(05)70250-7