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Communications should be addressed to: Dr. Louis; Department of Neurology; College of Physicians and Surgeons; Columbia University; Unit 198, Neurological Institute; 710 West 168th Street; New York, New York 10032.
GH Sergievsky Center, College of Physicians and Surgeons, Columbia University, New York, New YorkDepartment of Neurology, College of Physicians and Surgeons, Columbia University, New York, New YorkDepartment of Epidemiology, Mailman School of Public Health, Columbia University, New York, New YorkTaub Institute for Research on Alzheimer's Disease and the Aging Brain, College of Physicians and Surgeons, Columbia University, New York, New York
Department of Population and Family Health, Mailman School of Public Health, Columbia University, New York, New YorkColumbia Center for Children's Environmental Health, Mailman School of Public Health, Columbia University, New York, New York
Department of Population and Family Health, Mailman School of Public Health, Columbia University, New York, New YorkColumbia Center for Children's Environmental Health, Mailman School of Public Health, Columbia University, New York, New York
There have been virtually no surveys of the prevalence, clinical features, or correlates of tremor in children and none in the United States.
Methods
A total of 317 children (age 11.0 ± 1.1 years; range, 9.0 to 14.7) underwent an evaluation at one time point. Each drew Archimedes spirals, which were rated by a senior neurologist specializing in movement disorders.
Results
A spiral score of 1 (mild but consistent tremor) was present in either hand in 105 (33.1%) children; a higher score (1.5, mild-to-moderate tremor) was present in either hand in 7 (2.2%) children. Higher spiral scores were associated with poorer motor hand function as assessed using the Purdue Pegboard test. Spiral scores were higher in boys than girls, were inversely associated with age, and were higher in the nondominant than dominant hand. Spiral scores were highest in children who were taking psychiatric medications and in children with psychiatric or neurological disorders.
Conclusions
Mild tremor is common in children and covaries significantly with several demographic and clinical factors as well as usage of certain medications. It also lessens with advancing age. Rather than an isolated finding, tremor was associated with other measures of poorer motor hand function.
The focus of tremor research has almost exclusively been on adult populations. Curiously, there have been virtually no surveys of the prevalence, clinical features, or correlates of tremor among children.
Hence, the health of this age group, which also forms the core of the future adult population, is of considerable importance. A prospective population-based study of environmental exposures and neurocognitive development was conducted in New York city children.
We used this opportunity to study tremor in more than 300 such children, all of whom drew spirals with each hand, from which tremor was systematically quantified by a senior movement disorders neurologist using a published clinical rating scale.
The subjects for this report were participants in an ongoing prospective cohort study (Columbia Center for Children's Environmental Health) of inner-city mothers and their newborn infants
The cohort study was initiated in 1997 to evaluate the effects of common ambient exposures on neurocognitive development in a cohort of newborns from low-income communities in New York City. The study was approved by the Institutional Review Board of Columbia University. Informed consent was obtained from all mothers and, informed assent, from all children (starting at age 7 years).
Of 725 pregnant women, who consented to participate in the study and gave birth between 1997 and 2007, 535 mother-child dyads were retained in the full cohort at the time of this report. Of these children, 317 had the following: (1) reached at least 9 years of age; (2) maternal or cord blood samples at delivery; (3) postnatal sociodemographic and biomedical covariates; (4) neurodevelopmental outcomes; and (5) one set of hand-drawn spirals (as described in the following).
Study assessment
The in-home, yearly evaluation of mother-child dyads was conducted by a trained tester and included the collection of demographic data as well as data on medical diagnoses (e.g., epilepsy, attention deficit hyperactivity disorder [ADHD], depression, asthma), learning disorders, and medications. This included medications taken for any psychiatric or neurological condition (e.g., depression, ADHD, epilepsy) or for any medical condition (e.g., asthma).
During their most recent yearly assessment, each child was also asked to draw five spirals: a practice Archimedes spiral with their dominant hand followed by four additional spirals (two with dominant hand followed by two with nondominant hand). Spirals were drawn on a standard 8.5 × 11 inch sheet of paper using a pen or pencil while the participant was seated at a table. The paper was centered at right angles directly in front of them and held down by their other hand. The drawing hand was not allowed to rest or be supported when the spiral was being drawn. Participants started at the center of the page, without lifting their pen or pencil. The practice spiral was drawn in between the lines of a standardized, predrawn, photocopied, spiral. The remaining spirals were drawn free hand on a blank sheet of paper.
Tremor in these five spiral drawings was later rated by a senior neurologist specializing in movement disorders (E.D.L.) who was blinded to all clinical information. Tremor ratings, published previously,
for each spiral were as follows: 0 (no tremor), 0.5 (subtle, low amplitude oscillations are present in a few spots but are not consistently present throughout the spiral), 1.0 (low amplitude oscillations are present in multiple places), 1.5 (low amplitude oscillations are present in multiple places and oscillations can at times reach moderate amplitude), and 2 (moderate amplitude oscillations present throughout the spiral; for examples of rated spirals, see Figures 2, 3, and 4 in Louis et al.
and Figure). We have previously demonstrated in a study in which 200 spirals were rated by four raters that the inter-rater agreement between the senior movement disorder and three other raters was high (interclass correlation coefficients = 0.67 to 0.74, P < 0.001).
Screening for action tremor in epidemiological field surveys: assessing the reliability of a semi-quantitative, visual, template-based scale for rating hand-drawn spirals.
Tremor Other Hyperkinet Mov (N Y).2012; 2 (pii: tre-02-46-177-2)
During spiral rating, the neurologist was careful to distinguish clear, regular, oscillations from sloppiness, spatial errors, and other irregularities, or movement disfluencies that were not strictly oscillatory. There were three spiral scores for each child as follows: the spiral score of the practice spiral, the spiral score in the dominant hand (the average of the two ratings), and the spiral score in the nondominant hand (the average of the two ratings).
FigureExamples of spirals given ratings of 0 to 1.5 (A-D). (A) Rating = 0 (no tremor). (B) Rating = 0.5 (subtle, low amplitude oscillations are present in a few spots [see arrows] but are not consistently present throughout the spiral). (C) Rating = 1.0 (low amplitude oscillations are present in multiple places). (D) Rating = 1.5 (low amplitude oscillations are present in multiple places and oscillations can at times reach moderate amplitude).
To further evaluate the performance of hand motor function, each child performed the Purdue Pegboard test, which measured gross movements of hands, fingers and arms, and fingertip dexterity in assembly tasks. The child was asked to place small metal pegs in holes in a 30 second practice trial. This was followed by two 30 second trials with each hand separately and two 30 second trials with both hands simultaneously. A stopwatch was used for administration of the test, and the number of pegs placed was recorded. The Purdue pegboard test score was the average of the two trials that used both hands simultaneously.
The three spiral scores were not normally distributed (Kolmogorov-Smirnov tests <0.05); therefore, nonparametric tests (e.g., Mann-Whitney test, Spearman r) were used in analyses of these three variables. All analyses were performed in SPSS version 21.0 (Chicago, IL).
Results
There were 317 children (mean age, 11.0 ± 1.1 years; range, 9.0 to 14.7 years; Table 1). A spiral score of 1 (mild but consistent tremor) was present in either hand in 105 (33.1%) children, in the dominant hand in 40 (12.6%) children, in the nondominant hand in 94 (29.7%) children and in both hands in 29 (9.1%) children. A higher score (1.5, mild-to-moderate tremor) was present in the dominant hand in 0 (0.0%) children and in the nondominant hand in 7 (2.2%) children. No children had scores of ≥2.
Table 1Demographic and Clinical Characteristics of 317 Children
The mean spiral score was 0.56 ± 0.39 in the nondominant hand and 0.41 ± 0.33 in the dominant hand (Table 1). In 117 (36.9%) of 317 children, the nondominant spiral score was greater than the dominant spiral score, and in 170 (53.6%), they were equal. In only 30 (9.5%) was the dominant spiral score greater than the nondominant spiral score.
Boys had higher spiral scores than girls; the difference in the spiral score on the practice spiral reached statistical significance (Table 2).
Age was inversely associated with the spiral score in the dominant arm (Spearman r = −0.20, P < 0.001), the spiral score in the nondominant arm (Spearman r = −0.12, P = 0.03), and the score on the practice spiral (Spearman r = −0.19, P = 0.001; i.e., with older age, there was a significant reduction in spiral scores).
Approximately 15% of the children were taking medication. The spiral score in the nondominant hand was highest in children who were taking a psychiatric medication (Table 3). Spiral scores did not vary by use of asthma medication (Table 3).
Slightly more than 6% of the children had symptoms of a psychiatric disorder, with the most common being ADHD, followed by depression, or a neurological disorder, with the most common being epilepsy, and their spiral test scores were higher than those of children without comorbidity (Table 4, top rows). This difference was not because of the effects of medication; when we restricted the analysis to children who were not taking medication, the differences largely persisted, although the power of these analyses was reduced (Table 4, bottom rows). Children with learning disorders did not differ to a significant degree from those without comorbidity in terms of their spiral scores (Table 4).
The mean spiral score of the practice spiral was 0.48 ± 0.39 (Table 1). In 84 (27.6%) of 304 children who provided practice spirals, the mean practice spiral score was greater than the mean dominant spiral score, in 174 (57.2%) they were equal, and in only 46 (15.1%) was the mean dominant spiral score greater than the mean practice spiral score.
The score on the Purdue pegboard test score was inversely correlated with the score on the practice spiral (Spearman r = −0.14, P = 0.03) and trended toward a similar inverse correlation with both the dominant and nondominant spiral scores (for both, Spearman r = −0.11, P = 0.08; i.e., greater tremor was associated with fewer correct peg placements).
Discussion
There have been few studies of tremor in children. We studied more than 300 boys and girls (mean age = 11.0 years) living in New York city. Higher tremor scores (1.5, mild-to-moderate tremor) were present in few children (7, 2.2%).
However, milder tremor (rating of 1) was present in both hands in approximately one in 10 children (i.e., 29, 9.1%), indicating that there is some measurable tremor in this age group.
The tremor was associated with poorer motor dexterity (i.e., poorer motor hand function) as assessed using the Purdue Pegboard test.
There have been few previous systematic studies of tremor in children and none in the United States. In a prior study we assessed tremor, using spirals, in more than 800 schoolchildren living in Spain.
In that study, however, we were not able to assess in detail the effects of medications or medical comorbidity. In a study of 311 children aged 11 to 14 in Valcamonica, Italy, tremor was measured by accelerometry,
although tremor was not the focus of that study and its attendant analyses. An accelerometric study of tremor in 287 children aged 2 to 16 years was conducted in England in 1959.
However, that study focused on the effects of age on tremor frequency. Tremor amplitude was not assessed nor were gender differences or side to side differences.
Approximately 15% of the children in our cohort were taking medication. Spiral scores were highest in children who were taking psychiatric medications, with this effect most pronounced in the nondominant hand. Although numerous medications produce mild tremor, and some of the tremor we observed could have been because of medication, we also found that children with psychiatric or neurological disorders had higher spiral test scores than those without such comorbidities, and this seemed to be independent of medication. These data suggest that these disorders might themselves be associated with subtle motor system manifestations.
Tremor was greater in the nondominant hand than in the dominant hand. This side-side difference has been demonstrated in numerous studies of adults
Motor control, in general, is superior in the dominant than in the nondominant arm, and this is one possible explanation. Motor ability in the nondominant arm likely reflects more of a raw physiologic state whereas motor output in the dominant arm also reflects a trained state. Of related interest is that tremor in our cohort lessened with advancing age. This might be the result of improving motor performance with age.
The tremor was associated with poorer motor hand function as assessed using the Purdue Pegboard test, indicating either that the tremor itself resulted in some reduction in dexterity or that both the tremor and the loss of dexterity were a result of an underlying perturbed motor state.
This study had limitations. We recognize that tremor was assessed using a clinical scale rather than accelerometry. In spite of this, the method we used is very sensitive. Our data in other studies
have indicated that spiral drawings are a reasonably sensitive measure of tremor, as 97.0% of individuals with mild or greater tremor on a more detailed tremor examination exhibited ratings of 0.5 in one or more hands during spiral drawing. Second, the current results reflect a sample of low-income children in New York city, and future studies should assess whether they may be generalized to other cohorts. Third, the spiral assessment was at one point in time rather than longitudinal; additional follow-up studies are needed. Finally, although the reliability of the rating scale has been demonstrated, the raters were not child neurologists, and it would be useful to conduct a reliability study among a group of pediatric neurologists. This study also had considerable strengths including the assessment of tremor in more than 300 children in a systematic way, the evaluation of spirals by a clinically-blinded senior neurologist specializing in movement disorders and the ability to assess tremor in relation to a number of important clinical correlates including age, gender, medications, and medical comorbidities.
Mild tremor is common in children. It covaries significantly with several demographic and clinical factors as well as usage of certain medications. It also lessens with advancing age. Rather than an isolated finding, tremor was associated with other measures of poorer motor hand function.
Dr. Louis has received research support from the National Institutes of Health: NINDS #R01 NS042859 (principal investigator), NINDS #R01 NS39422 (principal investigator), NINDS #R01 NS086736 (principal investigator), NINDS #R01 NS073872 (principal investigator), NINDS #R01 NS085136 (principal investigator), NINDS #T32 NS07153-24 (principal investigator), NINDS #R21 NS077094 (co-Investigator), and NINDS #R01 NS36630 (co-Investigator). He has also received support from Parkinson's Disease Foundation, the Arlene Bronstein Essential Tremor Research Fund (Columbia University), and the Claire O'Neil Essential Tremor Research Fund (Columbia University). He also acknowledges the support of National Institute of Environmental Health Sciences P30 ES09089 and the Irving Institute for Clinical and Translational Research: UL1 TR000040. Dr. Rauh has received research support for this work from the National Institutes of Health: National Institute of Environmental Health Sciences #R01 ES015579 (principal investigator), National Institute on Drug Abuse #R01 DA027100 (principal investigator), National Institute of Environmental Health Sciences #P01 ES09600, EPA RD-83214101 (co-investigator), and #R01 ES015282 (co-investigator).
References
Louis E.D.
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How normal is ‘normal’? Mild tremor in a multiethnic cohort of normal subjects.
Screening for action tremor in epidemiological field surveys: assessing the reliability of a semi-quantitative, visual, template-based scale for rating hand-drawn spirals.
Tremor Other Hyperkinet Mov (N Y).2012; 2 (pii: tre-02-46-177-2)
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