PEDIATRICS Vol. 114 No. 5 November 2004, pp. 1203-1205 (doi:10.1542/peds.2004-0031)
Essential Tremor Among Children
From the Department of Neurology, Parkinson’s Disease Center and Movement Disorders Clinic, Baylor College of Medicine, Houston, Texas
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ABSTRACT |
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Objective. To characterize the clinical and therapeutic aspects of essential tremor (ET) among children.
Background. ET, an autosomal dominant disorder, has been studied extensively among adults, but little is known regarding its occurrence, clinical characteristics, treatment, and prognosis in pediatric populations. Often stigmatized as a disorder of the elderly, ET may be misdiagnosed among children. Previous studies of childhood-onset ET were limited by small sample sizes.
Methods. Clinical data, including gender, age at onset, family history, associated disorders, and response to treatment, were collected for consecutive patients diagnosed with childhood-onset ET at the Movement Disorders Clinic at Baylor College of Medicine.
Results. Of the 39 patients with ET, 29 (74.4%) were male. The mean age at onset was 8.8 ± 5.0 years, and the mean age at evaluation was 20.3 ± 14.4 years. A family history of tremor was noted for 79.5% of the patients. Eighteen (46.2%) had some neurologic comorbidity, such as dystonia, which was noted for 11 patients (28.2%). Only 24 of the patients (61.5%) were treated with a specific antitremor medication; 5 of the 12 patients treated with propranolol experienced improvement.
Conclusions. Concomitant movement disorders, such as dystonia, are common among patients with childhood-onset ET, which supports the concept that ET is a heterogeneous disorder. Treatment strategies used for adult patients with ET seem to be effective also for children with ET, although controlled therapeutic trials in this population of patients with ET are lacking.
Key Words: tremor • essential tremor • dystonia
Abbreviations: ET, essential tremor
Essential tremor (ET) has been studied extensively among adults, but little is known regarding its occurrence, clinical features, treatment, and prognosis in pediatric populations. Hornabrook and Nagurney1 reported that 4.6% of cases of ET had their onset during childhood. Because it is often stigmatized as a disorder of the elderly, ET may be misdiagnosed among children. Furthermore, the study of childhood-onset ET may provide new insights into the genetic features of this common disorder. ET is thought to be inherited as an autosomal dominant disorder, although no gene mutations have yet been identified.2–4 Previous reports focusing on ET among children included relatively small numbers of cases, ranging from 5 to 19.5–7
The primary purpose of this study is to draw attention to ET not only as an adult or "senile" condition but also as an important and potentially troublesome or even disabling pediatric movement disorder. With a relatively large sample of childhood-onset ET cases, the findings provide new insights into the clinical presentation, treatment, and pathogenesis of this common movement disorder.
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METHODS |
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All patients diagnosed with ET that started at <18 years of age were identified from the database at the Movement Disorders Clinic at Baylor College of Medicine. This yielded 42 candidates but 3 patients were excluded, because of a psychogenic component for 1 and insufficient information for 2. ET was defined as bilateral postural tremor, with or without kinetic tremor involving the hands or forearms, that was visible and persistent.2 Some patients had "pure" ET, without associated disorders, whereas others had coexistent dystonia and possibly other movement disorders.
We analyzed various features of the childhood-onset ET, including age at onset of tremor, anatomic location of tremor, and nature of tremor (postural, kinetic, task-specific, or rest tremor). Postural tremor, defined as an oscillatory movement with the body part being held against the force of gravity, was assessed while the arms were held outstretched in front of the body or in a "wing-beating" position, ie, horizontal with the shoulders abducted and the elbows flexed. Kinetic tremor was elicited with voluntary finger-to-nose and heel-to-shin movements. Task-specific tremors were evaluated during the particular activity, such as writing, that precipitated the tremor. Rest tremor was assessed while the affected limb was in a resting position, supported against gravity. Family histories were obtained from the patients and the parents, and the family members were examined whenever possible. If information was not available in the charts, patients or their parents were contacted by telephone.
SPSS version 12.0 (SPSS, Chicago, IL) was used for analysis of the data, and Student’s t test and Fisher’s exact test were used to determine significant differences among variables. 
2 analysis was used to determine differences between genders with respect to anatomic distribution and type of tremor.
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RESULTS |
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Of the 39 patients with ET, 29 (74.4%, P = .003) were male (Table 1). The mean age at onset was 8.8 ± 5.0 years (range: 1–16 years), and the mean age at evaluation was 20.3 ± 14.4 years (range: 3.3–64.4 years). Twenty-seven of 39 patients (69.2%) reported a first-degree relative with tremor, and another 23 of 29 patients (79.3%) reported a relative beyond the first degree with tremor. Overall, 31 patients (79.5%) reported at least 1 relative with tremor. There were no significant differences between male and female patients with respect to anatomic distribution or the nature of tremor (Table 2). Twenty of the 39 cases (51.3%) were diagnosed as pure ET, without any other neurologic disorder; the reminder of the cases involved a variety of comorbidities. In addition to dystonia, which was noted for 11 patients (28.2%), Tourette syndrome, manifested by motor and phonic tics, attention deficit disorder, and obsessive-compulsive disorder, was a frequent comorbidity, noted for 9 patients (23.1%). The frequent occurrence of Tourette syndrome among our patients with childhood-onset ET might be an artifact, however, because these boys were initially referred for evaluation of Tourette syndrome and the ET was coincidentally diagnosed on the basis of our examination and history results.
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The amplitude of ET may be influenced by many factors. Twenty of the 39 patients (51.3%) noted that stress or anxiety increased their tremor. All 11 patients who responded to questions about physical activity noted that this increased their tremor. Five male and 2 female patients noted that caffeine exacerbated their tremor; 5 patients (2 male and 3 female patients) noted that alcohol intake transiently relieved their tremor.
Only 24 of the 39 patients were treated with specific antitremor medication. Of the 12 patients treated with propranolol, 5 continued treatment and noted marked improvement in their tremor. Two of the 9 patients treated with primidone also noted improvement with the drug.
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DISCUSSION |
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In a previous study of 350 patients with ET who were evaluated in our clinic, we found a bimodal distribution of the age at onset of ET, with peaks in the second and sixth decades,3 a finding confirmed by Bain et al.4 Both studies found no difference in clinical features between the young-onset and late-onset groups. The findings from the present report of 30 patients with childhood-onset ET provide additional evidence that childhood-onset ET is clinically and phenomenologically similar to the more common adult-onset ET.
Most of our patients with ET were boys (P = .003), similar to the findings of Louis et al7 in the second largest study of childhood-onset ET (N = 19). Louis et al7 found no major difference between childhood-onset and adult-onset tremor except for male preponderance and a paucity of head tremor in the childhood-onset ET group. We also found that head tremor was relatively uncommon in our population, being noted for only 7 of 39 patients (17.9%), 5 male and 2 female patients. This is in contrast to adult head tremor, which is noted predominantly for female patients with ET, being found for 60% of women with ET.8 All of our patients had hand tremor and 38.4% also exhibited arm tremor; 26 of 39 patients (66.7%) had a task-specific tremor (for example, while playing baseball or playing with toys). Tremor in the head, voice, legs, and trunk was noted for far fewer patients than was upper-extremity tremor.
Our finding that 79.5% of all patients had a family history of tremor must be interpreted cautiously, because this information was based largely on questioning of the patients and their parents, rather than on actual examination of all relatives. Our findings, however, are consistent with those of Louis et al,7 who found a family history of tremor for 68.2% of their patients. The high rate of familial occurrence provides support for a genetic basis of ET. Although the gene for this disorder has been elusive, a gene marker on chromosome 2p22-p25 has been identified.9
The most frequently associated neurologic disorder in our series was dystonia. This correlates with findings for adult ET cases, for which the frequency of ET with associated dystonia has been reported to be as high as 47%.3 Although some experts view ET as a monosymptomatic disorder,10 we consider it a heterogeneous disorder that may be monosymptomatic in some families but may be associated with coexistent disorders such as dystonia and parkinsonism in other families.2,11 Additional genetic studies may clarify this issue. As noted above, the high incidence of Tourette syndrome in our series is probably an artifact, because the children with coexistent ET and Tourette syndrome were initially referred for evaluation of the latter disorder.
Although none of our children’s parents recalled tremor during infancy or among family members, the onset of tremor may be preceded by so-called "shuddering attacks" for some children with ET.12,13 Vanasse et al12 identified 6 young children who presented with a history of shuddering attacks and exhibited postural tremor on examination, with a positive family history of tremor. These attacks were described as episodes of "shivering" during which the child remained conscious, with the head, elbows, and knees flexed.12,13 Electroencephalographic monitoring and evaluation of patients with shuddering attacks reveal no abnormal findings, which distinguishes this disorder from epilepsy.13 These studies suggest that shuddering attacks, occurring as early as during infancy, herald the onset of ET, dystonia, or both later in life.14
Among patients who received treatment purely for tremor, propranolol was the drug most commonly prescribed at the initial consultation. The positive response to propranolol noted by 5 of our patients is consistent with the known efficacy of this ß-receptor blocker in adult tremor.
Because all patients were referred to our specialty clinic, they may not be representative of the general pediatric ET population. Patients who experience tremor but do not seek medical attention or are not diagnosed and therefore not referred to a specialty clinic are not represented, with consequent selection bias toward more severe or complicated cases. The observation of ET among patients originally referred for evaluation and treatment of Tourette syndrome, however, underscores the lack of diagnostic acumen with respect to ET among children among primary care physicians, particularly pediatricians. Our study should draw attention to ET as an important and potentially troublesome pediatric movement disorder.
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FOOTNOTES |
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Accepted May 20, 2004.
Address correspondence to Joseph Jankovic, MD, Department of Neurology, Parkinson’s Disease Center and Movement Disorders Clinic, Baylor College of Medicine, 6550 Fannin St, Suite 1801, Houston, TX 77030. E-mail: josephj{at}bcm.tmc.edu
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PEDIATRICS (ISSN 1098-4275). ©2004 by the American Academy of Pediatrics
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