Tremors

Dystonic Tremor: Time to Change

BACKGROUND

The term dystonic tremor is being increasingly used in neurological publications despite uncertainties about its meaning. We provide here a historical reconstruction from its original introduction in 1984 to help distinguish dystonia from essential tremor.

METHODS

A comprehensive Pubmed search of MeSH terms "dystonia", "tremor", and "essential tremor" provided the information base for reconstructing historical usage of the term "dystonic tremor".

RESULTS

Over the years, this expression was enriched of additional meanings and sided by companion descriptors, such as tremor associated with dystonia. Dystonic tremor has been considered characteristically coarse, jerky, irregular, directional and asymmetrical. These characteristics, however, are not included in the most recent definitions of tremor. The relationship between tremor and dystonia is not easy to untangle, as the two phenomena are often recognized in association. Tremor and dystonia experts have developed different visions of dystonic tremor that have been variably implemented. There are currently two independent consensus definitions, which are not coincident and imply different pathophysiological interpretations.

CONCLUSIONS

This historical reappraisal highlights that usage of the expression dystonic tremor has evolved over time to lose its original meaning. Notwithstanding inconsistencies of current definitions, its usage has steadily increased and it is time now to agree on an updated terminology.

Chronic mercury exposure examined with a computer-based tremor system

Tremor is being increasingly evaluated by quantitative computer-based systems to differentiate its causes. In this study, a group of mercury-exposed workers were assessed to determine whether tremor characteristics differed by exposure level. Workers were classified into two groups: those with an average urine mercury concentration below the American Conference of Government Industrial Hygienist Biological Exposure Index of 35 micrograms/g creatinine, and those with an average urine mercury concentration above the Biological Exposure Index. Tremor characteristics (including intensity, harmonic index, center frequency, standard deviation of the center frequency, and tremor index) were measured and recorded with a computer-based tremor system. Sixteen of 17 workers who were potentially exposed to mercury participated in the study. Three workers had a mean urine mercury concentration of 27.0 micrograms/g-creatinine and were assigned to the low-exposure group, and 13 workers had a mean urine mercury concentration of 200.2 micrograms/g-creatinine and were assigned to the high-exposure group. There was a statistically significant difference in the tremor index (which compiles five individual tremor parameters into a single value) between the two groups (P = 0.04; Wilcoxon's rank sum test). Other tremor characteristics did not differ significantly between the groups. Tremor index may be more useful than measures of individual tremor parameters in differentiating normal from subclinical pathological tremors among groups of workers with chronic mercury exposure.

Classification of normal and pathological tremors using a multidimensional electromagnetic system

A new multidimensional movement analysis system was used to record limb tremor over six degrees-of-freedom, and signal processing techniques were explored to develop a suitable classification method to distinguish between different types of tremor. The specific aims were to investigate the ability of the system to screen for differences between normal subjects and a group of neurological patients, and then to differentiate between three diagnostic groups of patients. Postural tremor at the hand was recorded in normal subjects (n=24) and patients with essential tremor (n=21), multiple sclerosis (n=17) and parkinsonism (n=19). Data were collected using a 3Space Fastrak((R)) (Polhemus, Inc.) over six degrees-of-freedom (three translational directions and three rotations). Spectral estimates produced measures of tremor frequency and amplitude. Mathematical models of the data, using autoregressive modelling and K-nearest neighbour classification, produced parameters used to classify, (1) the normal subjects and 24 patients (using the three rotational movements), and (2) the three patient groups (using all six movement directions). Results were given in terms of the probability of each subject belonging to the groups being classified. 70%). The diagnostic classification produced clear differences between the patient groups (60% for essential tremor, 80% for multiple sclerosis and 60% for parkinsonism). The ability of this assessment technique to distinguish between postural tremor in normal subjects and neurological patients suggests that it could be developed as a screening tool. Classification of tremors between the patients groups, with a high degree of sensitivity, indicates the potential for further development of the system as a diagnostic aid.

A preliminary assessment of the medical and functional factors associated with vehicle crashes by older adults

OBJECTIVES

To examine associations between medical and functional variables and at-fault car crashes in a cohort of older drivers.

DESIGN

A case-control study.

SETTING

A tertiary care medical center.

PARTICIPANTS

Older drivers (ages 55-90 years) residing in Jefferson County, Alabama (n = 174). Cases were drivers who had at least one at-fault crash in the previous 6 years; controls were crash-free during the same period.

MEASUREMENTS

Self-reported medical conditions, reported and observed functional measures, and urinary drug screens. The occurrence of one or more at-fault car crashes in the 6 years preceding the 1991 assessment date represented the outcome measure.

RESULTS

Ninety-nine older drivers experienced between one and seven at-fault vehicle crashes during the period 1985 through 1991, whereas 75 drivers did not. Logistic regression models indicated that the following variables were independently associated with crash involvement: A 40% or greater reduction in the useful field of view (OR = 6.1; 95% CI, 2.9 to 12.7; P < 0.001), black race (OR = 6.6; 95% CI, 1.7 to 26.2; P = .007), a history of falling in the previous 2 years (OR = 2.6; CI, 1.1 to 6.1; P = .025), and not taking a beta-blocking drug (OR = 4.3; CI, 1.2 to 15.0; P = .023).

CONCLUSIONS

Functional assessments, such as a comprehensive test of visual processing, a falls history, and a review of current medications may be of greater relevance than specific medical conditions in the identification of older at-risk drivers. If prospective studies determine that falling and crashing share risk factors, a unified approach to the prevention of these mobility disorders could result. The finding of an independent association of black race with at-fault crashing is in need of further clarification because of the low representation of black drivers in this sample.

Treating the progressive stages of Parkinson's disease

Parkinson's disease affects thousands of Americans, men and women equally and apparently with little regard to race. Its diagnosis depends largely on repeated clinical observations of representative signs, such as resting tremor, rigidity, bradykinesia, and gait disturbances. Patients progress through stages: Early disease involves only one limb or side and confers minimal disability, but advanced disease restricts patients to full care. Treatment is chosen on the basis of disease stage and patient response. Combination carbidopa-levodopa (Sinemet) is appropriate for any significant degree of disability, and other antiparkinsonian drugs and anticholinergic agents may be used as adjuncts. Electroconvulsive therapy, use of selegiline hydrochloride (Eldepryl), and surgery are still undergoing investigation but may hold promise.