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    The Most Cited Works in Essential Tremor and Dystonia

    Authors:

    Nicolas K. K. King,

    Division of Neurosurgery, University of Toronto, Toronto Western Hospital, Toronto, Ontario, CA
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    Joseph Tam,

    Division of Neurosurgery, University of Toronto, Toronto Western Hospital, Toronto, Ontario, CA
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    Alfonso Fasano,

    Morton and Gloria Shulman Movement Disorders Clinic and the Edmond J. Safra Program in Parkinson’s Disease, Movement Disorders Center, TWH, UHN, Division of Neurology, University of Toronto, Toronto, Ontario, CA
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    Andres M Lozano

    Division of Neurosurgery, University of Toronto, Toronto Western Hospital, Toronto, Ontario, CA
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    Abstract

    Background: The study of the most cited works in a particular field gives an indication of the important advances, developments, and discoveries that have had the highest impact in that discipline. Our aim was to identify the most cited works in essential tremor (ET) and dystonia.

    Methods: A bibliometric search was performed using the ISI Web of Science database using selected search terms for ET and dystonia for articles published from 1900 to 2015. The resulting citation counts were analyzed to identify the most cited works, and the studies were categorized.

    Results: Using the criterion of more than 400 citations, there were four citation classics for ET and six for dystonia. The most cited studies were those on pathophysiology followed by medical treatments, clinical classification, genetic studies, surgical treatments, review articles, and epidemiology studies. A comparison of the most cited articles for ET and dystonia showed that there was a divergence, with ET and dystonia having a higher number of epidemiologic and genetic studies, respectively. Whereas the peak period for the number of publications was 2000–2004 for ET, it was 1995–1999 for dystonia.

    Discussion: Given the large number of patients with these disorders, there appears to be an unmet need for further research advances in both areas, but particularly for ET as the most common movement disorder.

    Keywords: Essential tremor, dystonia, citation analysis
    How to Cite: King NKK, Tam J, Fasano A, Lozano AM. The Most Cited Works in Essential Tremor and Dystonia. Tremor and Other Hyperkinetic Movements. 2016;6:310. DOI: http://doi.org/10.5334/tohm.283
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      Published on 19 Apr 2016
    Peer Reviewed
     CC BY 4.0
     Accepted on 21 Mar 2016            Submitted on 26 Mar 2015

    Introduction

    The study of the most cited works in a particular field gives an indication of the most impactful advances, developments, and discoveries that have been instrumental in driving research in that discipline.1,2 This analysis also offers insight into where the field has been, where the unmet needs are, and where the field may be heading.1 Such snapshots of the most important works have previously been generated for several areas of neurology and neurosurgery.1,3–8 A recent study examined citations related to essential tremor (ET),8 but a similar analysis has however not yet been carried out for dystonia. Importantly, no study has compared the literature in the two different but linked fields of ET and dystonia. Here we compared and contrasted these two research areas to produce a more comprehensive review and identify the most highly cited ET and dystonia articles.

    Methods

    We used a search strategy similar to one we have previously used for bibliometric analysis in other fields.1,9 A search was performed in January 2016 using the bibliometric database ISI Web of Science for articles published between 1900 and 2015 using the topic search terms “(essential OR benign OR familial) and tremor*” for ET. For dystonia, the search terms were “dystoni* OR meige syndrome OR writer cramp OR torticollis.” Alternative terms were also searched to identify additional citations: “professional cramp OR musician cramp OR eyelid opening apraxia OR Brueghel syndrome OR Oppenheim disease.” The “OR” is a Boolean operator to find records containing any of the terms, and the parentheses were used to define operator precedence such that the expression inside the parentheses is executed first. The asterisk was included as a wild card character. The search terms for ET returned 4,578 articles with the earliest published in 1903. The search terms for dystonia returned 18,839 articles with the earliest published in 1901. The two results were separately sorted by number of citations from highest to lowest and were manually examined to identify the top 100 cited articles related to the field. Articles were considered “citation classics” if they received 400 or more citations as previously defined.2

    Results

    We first conducted a broad search to identify the relative publication activity across each of the main movement disorders as identified by PubMed (Table 1). Relative to Parkinson’s disease (PD), the number of papers identified in PubMed on dystonia was approximately one fifth and on ET was approximately one twentieth.

    Table 1

    Number of Papers Available in PubMed for the Main Movement Disorders

    Disorder(Search Term)1 Number of Citations in PubMed (up to December 31, 2015)
    “Parkinson’s disease” 59,140
    “Essential tremor” 2,930
    “Dystonia” 12,978
    “Myoclonus” 8,969
    “Chorea” 6,742
    “Tic” 5,952
    “Tics” 3,502

    1

    Each search term was entered as indicated in PubMed for the period of January 1, 1900 to December 31, 2015.

    The 100 most cited articles showed that the number of citations per article for ET ranged from 79 to 846 (median 100) compared to a range from of 137 to 560 (median 179) for dystonia. The articles were ranked by citations, and those articles that were ranked in the top 100 are shown in Table 2 for ET and Table 3 for dystonia. Out of these articles, there were four citation classics receiving 400 or more citations for ET10–13 and six citation classics for dystonia,14–19 representing 0.09% and 0.03% of all search results, respectively.

    Table 2

    Summary of Top 100 articles for Essential Tremor (Ranked in Order of Citations)

    Absolute Number Rank Citations Paper Category
    1 1 846 Benabid AL, Pollak P, Gervason C, et al. Long-term suppression of tremor by chronic stimulation of the ventral intermediate thalamic nucleus. Lancet 1991;337:403–406 Clinical: Surgery
    2 2 809 Deuschl G, Bain P, Brin M. Consensus statement of the Movement Disorder Society on tremor. Mov Disord 1998;13 Supplement:2–23 Clinical: Classification
    3 3 652 Benabid AL, Pollak P, Gao DM, et al. Chronic electrical stimulation of the ventralis intermedius nucleus of the thalamus as a treatment of movement disorders. J Neurosurg 1996;84:203–214 Clinical: Surgery
    4 4 484 Schuurman PR, Bosch DA, Bossuyt PMM, et al. A comparison of continuous thalamic stimulation and thalamotomy for suppression of severe tremor. N Engl J Med 2000;342:461–468 Clinical: Surgery
    5 5 294 Koller W, Pahwa R, Busenbark K, et al. High-frequency unilateral thalamic stimulation in the treatment of essential and Parkinsonian tremor. Ann Neurol 1997;42:292–299 Clinical: Surgery
    6 6 291 Limousin P, Speelman JD, Gielen F, et al. Multicentre European study of thalamic stimulation in parkinsonian and essential tremor. J Neurol Neurosurg Psychiatry 1999;66:289–296 Clinical: Surgery
    7 7a 220 Louis ED, Ottman R, Hauser WA. How common is the most common adult movement disorder? Estimates of the prevalence of essential tremor throughout the world. Mov Disord 1998;13:5–10 Review
    8 7b 220 Critchley M. Observations on essential (heredo-familial) tremor. Brain 1949;72:113–139 Review
    9 8 215 Benabid AL, Benazzouz A, Hoffmann D, et al. Long-term electrical inhibition of deep brain targets in movement disorders. Mov Disord 1998;13 Supplement:119–125 Clinical: Surgery
    10 9 214 Bain PG, Findley LJ, Thompson PD, et al. A study of hereditary essential tremor. Brain 1994;117:805–824 Review
    11 10 212 Blond S, Caparros-Lefebvre D, Parker F, et al. Control of tremor and involuntary movement-disorders by chronic stereotaxic stimulation of the ventral intermediate thalamic nucleus. J Neurosurg 1992;77: 62–68 Clinical: Surgery
    12 11 212 Lou JS, Jankovic J. Essential tremor: clinical correlates in 350 patients. Neurology 1991;41:234–238 Clinical: Classification
    13 12 210 Louis ED, Faust PL, Vonsattel JP, et al. Neuropathological changes in essential tremor: 33 cases compared with 21 controls. Brain 2007;130:3297–3307 Lab: Patho-physiology
    14 13 198 Deuschl G, Raethjen J, Lindemann M, et al. The pathophysiology of tremor. Muscle Nerve 2001;24:716–735 Review
    15 15 177 Jenkins IH, Bain PG, Colebatch JG, et al. A positron emission tomography study of essential tremor: evidence for overactivity of cerebellar connections. Ann Neurol 1993;34:82–90 Lab: Patho-physiology
    16 15 174 Bain PG, Findley LJ, Atchison P, et al. Assessing tremor severity. J Neurol Neurosurg Psychiatry 1993;56:868–873 Clinical: Classification
    17 16 172 Brooks DJ, Playford ED, Ibanez V, et al. Isolated tremor and disruption of the nigrostriatal dopaminergic system: an 18F-dopa PET study. Neurology 1992;42:1554–1560 Lab: Patho-physiology
    18 17 169 Jankovic J, Cardoso F, Grossman RG, et al. Outcome after stereotaxic thalamotomy for parkinsonian, essential, and other types of tremor. Neurosurgery 1995;37:680–686 Clinical: Surgery
    19 18 167 Rajput AH, Offord KP, Beard CM, et al. Essential tremor in Rochester, Minnesota: a 45-year study. J Neurol Neurosurg Psychiatry 1984;47:466–470 Epidemiology
    20 19 166 Tasker RR. Deep brain stimulation is preferable to thalamotomy for tremor suppression. Surg Neurol 1998;49:145–153 Clinical: Surgery
    21 20 164 Benito-León J, Bermejo-Pareja F, Morales JM, et al. Prevalence of essential tremor in three elderly populations of central Spain. Mov Disord 2003;18:389–394 Epidemiology
    22 21a 158 Deuschl G, Wenzelburger R, Loffler K, et al. Essential tremor and cerebellar dysfunction: clinical and kinematic analysis of intention tremor. Brain 2000;123:1568–1580 Review
    23 21b 158 Louis ED. Essential tremor. Lancet Neurol 2005;4:100–110 Review
    24 22 154 Gulcher JR, Jonsson P, Kong A, et al. Mapping of a familial essential tremor gene, FET1, to chromosome 3q13. Nat Genet 1997;17:84–87 Lab: Genetic studies
    25 23 149 Koller WC, Busenbark K, Miner K, et al. The relationship of essential tremor to other movement-disorders: report on 678 patients. Ann Neurol 1994;35:717–723 Epidemiology
    26 24 142 Louis ED, Ferreira JJ. How common is the most common adult movement disorder? Update on the worldwide prevalence of essential tremor. Mov Disord 2010;25:534–541 Review
    27 25 138 Elble RJ. Physiological and essential tremor. Neurology 1986;36:225–231 Clinical: Classification
    28 26 131 Ondo W, Jankovic J, Schwartz K, et al. Unilateral thalamic deep brain stimulation for refractory essential tremor and Parkinson’s disease tremor. Neurology 1998;51:1063–1069 Clinical: Surgery
    29 27a 128 Geraghty JJ, Jankovic J, Zetusky WJ. Association between essential tremor and Parkinson’s disease. Ann Neurol 1985;17:329–333 Epidemiology
    30 27b 128 Winkler GF, Young RR. Efficacy of chronic propranolol therapy in action tremors of familial, senile or essential varieties. New Engl J Med 1974;290:984–988 Clinical: Medicine
    31 28a 127 Higgins JJ, Pho LT, Nee LE. A gene (ETM) for essential tremor maps to chromosome 2p22–p25. Mov Disord 1997;12:859–864 Review
    32 28b 127 Koller WC, Lyons KE, Wilkinson SB, et al. Long-term safety and efficacy of unilateral deep brain stimulation of the thalamus in essential tremor. Mov Disord 2001;16:464–468 Clinical: Surgery
    33 29 126 Colebatch JG, Findley LJ, Frackowiak RSJ, et al. Preliminary-report: activation of the cerebellum in essential tremor. Lancet 1990;336:1028–1030 Lab: Patho-physiology
    34 30a 125 Rehncrona S, Johnels B, Widner H, et al. Long-term efficacy of thalamic deep brain stimulation for tremor: Double-blind assessments. Mov Disord 2003;18:163–170 Clinical: Surgery
    35 30b 125 Wills AJ, Jenkins IH, Thompson PD, et al. Red nuclear and cerebellar but no olivary activation-associated with essential tremor: a positron emission tomographic study. Ann Neurol 1994;36:636–642 Lab: Patho-physiology
    36 31 123 Zesiewicz TA, Elble R, Louis ED, et al. Practice parameter: Therapies for essential tremor – Report of the quality standards subcommittee of the American Academy of Neurology. Neurology 2005;64:2008–2020 Clinical: Classification
    37 32a 121 Bucher SF, Seelos KC, Dodel RC, et al. Activation mapping in essential tremor with functional magnetic resonance imaging. Ann Neurol 1997;41:32–40 Lab: Patho-physiology
    38 32b 121 Stolze H, Petersen G, Raethjen J, et al. The gait disorder of advanced essential tremor. Brain 2001;124:2278–2286 Clinical: Classification
    39 33a 118 Benito-León J, Louis ED. Essential tremor: emerging views of a common disorder. Nat Clin Pract Neurol 2006;2:666–678 Review
    40 33b 118 Dogu O, Sevim S, Camdeviren H, et al. Prevalence of essential tremor – Door-to-door neurologic exams in Mersin Province, Turkey. Neurology 2003;61:1804–1806 Epidemiology
    41 34a 116 Benamer HTS, Patterson J, Grosset DG, et al. Accurate differentiation of Parkinsonism and essential tremor using visual assessment of [I-123]-FP-CIT SPECT imaging: The [I-123]-FP-CIT study group. Mov Disord 2000;15:503–510 Clinical: Classification
    42 34b 116 Rautakorpi I, Takala J, Marttila RJ, et al. Essential tremor in a Finnish population. Acta Neurol Scand 1982;66:58–67 Epidemiology
    43 35 115 Louis ED, Ottman R, Ford B, et al. The Washington Heights-Inwood Genetic Study of Essential Tremor: Methodologic issues in essential-tremor research. Neuroepidemiology 1997;16:124–133 Lab: Genetic studies
    44 36 113 Critchley E. Clinical manifestations of essential tremor. J Neurol Neurosurg Psychiatry 1972;35:365–372 Clinical: Classification
    45 37a 112 Lombardi WJ, Woolston DJ, Roberts JW, et al. Cognitive deficits in patients with essential tremor. Neurology 2001;57:785–790 Clinical: Classification
    46 37b 112 Benito-León J, Louis ED, Bermejo-Pareja F. Population-based case-control study of cognitive function in essential tremor. Neurology 2006;66:69–74 Epidemiology
    47 38 102 Jankovic J, Schwartz K, Clemence W, et al. A randomized, double-blind, placebo-controlled study to evaluate botulinum toxin type A in essential hand tremor. Mov Disord 1996;11:250–256 Clinical: Medicine
    48 39a 101 Wilms H, Sievers J, Deuschl G. Animal models of tremor. Mov Disord 1999;14:557–571 Review
    49 39b 101 Bain P, Brin M, Deuschl G, et al. Criteria for the diagnosis of essential tremor. Neurology 2000;54:S7–S7 Clinical: Classification
    50 39c 101 Sydow O, Thobois S, Alesch F, et al. Multicentre European study of thalamic stimulation in essential tremor: a six year follow up. J Neurol Neurosurg Psychiatry 2003;74:1387–1391 Epidemiology
    51 40a 99 Asenbaum S, Pirker W, Angelberger P, et al. [I-123]beta-CIT and SPECT in essential tremor and Parkinson’s disease. J Neural Transm (Vienna) 1998;105:1213–1228 Clinical: Classification
    52 40b 99 Growdon JH, Shahani BT, Young RR. Effect of alcohol on essential tremor. Neurology 1975;25:259–262 Lab: Patho-physiology
    53 40c 99 Alesch F, Pinter MM, Helscher RJ, et al. Stimulation of the ventral intermediate thalamic nucleus in tremor dominated Parkinson’s disease and essential tremor. Acta Neurochir (Wien) 1995;136:75–81 Clinical: Surgery
    54 41 98 Hornabrook RW, Nagurney JT. Essential tremor in Papua, New Guinea. Brain 1976;99:659–672 Epidemiology
    55 42a 97 Rajput AH, Rozdilsky B, Ang L, et al. Clinicopathological observations in essential tremor: report of 6 cases. Neurology 1991;41:1422–1424 Lab: Patho-physiology
    56 42b 97 Lee RG, Stein RB. Resetting of tremor by mechanical perturbations – a comparison of essential tremor and Parkinsonian tremor. Ann Neurol 1981;10:523–531 Clinical: Medicine
    57 43 96 Marshall J. Observations on essential tremor. J Neurol Neurosurg Psychiatry 1972;25:122–125 Clinical: Classification
    58 44a 95 Gironell A, Kulisevsky J, Barbanoj M, et al. A randomized placebo-controlled comparative trial of gabapentin and propranolol in essential tremor. Arch Neurol 1999;56:475–480 Clinical: Medicine
    59 44b 95 Louis ED, Zheng W, Jurewicz EC, et al. Elevation of blood beta-carboline alkaloids in essential tremor. Neurology 2002;59:1940–1944 Lab: Patho-physiology
    60 44c 95 Singer C, Sanchezramos J, Weiner WJ. Gait abnormality in essential tremor. Mov Disord 1994;9:193–196 Clinical: Classification
    61 44d 95 Benito-León J, Bermejo-Pareja F, Louis ED. Incidence of essential tremor in three elderly populations of central Spain. Neurology 2005;64:1721–1725 Epidemiology
    62 44e 95 Raethjen J, Lindemann M, Schmaljohann H, et al. Multiple oscillators are causing Parkinsonian and essential tremor. Mov Disord 2000;15:84–94 Lab: Patho-physiology
    63 44f 95 Stefansson H, Steinberg S, Petursson H, et al. Variant in the sequence of the LINGO1 gene confers risk of essential tremor. Nat Genet 2009;41:277–279 Lab: Genetic studies
    64 45a 94 Busenbark KL, Nash J, Nash S, et al. Is essential tremor benign? Neurology 1991;41:1982–1983 Epidemiology
    65 45b 94 Louis ED, Shungu DC, Chan S, et al. Metabolic abnormality in the cerebellum in patients with essential tremor: a proton magnetic resonance spectroscopic imaging study. Neurosci Lett 2002;333:17–20 Lab: Patho-physiology
    66 45c 94 Hariz MI, Shamsgovara P, Johansson F, et al. Tolerance and tremor rebound following long-term chronic thalamic stimulation for parkinsonian and essential tremor. Stereotact Funct Neurosurg 1999;72:208–218 Clinical: Surgery
    67 46a 93 Kumar R, Lozano AM, Sime E, et al. Long-term follow-up of thalamic deep brain stimulation for essential and Parkinsonian tremor. Neurology 2003;61:1601–1604 Clinical: Surgery
    68 46b 93 Boecker H, Wills AJ, Ceballos-Baumann A, et al. The effect of ethanol on alcohol responsive essential tremor: a positron emission tomography study. Ann Neurol 1996;39:650–658 Lab: Patho-physiology
    69 47a 92 Louis ED, Barnes L, Albert SM, et al. Correlates of functional disability in essential tremor. Mov Disord 2001;16:914–920 Clinical: Classification
    70 47b 92 Hubble JP, Busenbark KL, Wilkinson S, et al. Deep brain stimulation for essential tremor. Neurology 1996;46:1150–1153 Clinical: Surgery
    71 47c 92 Rajput A, Robinson CA, Rajput AH. Essential tremor course and disability – A clinicopathologic study of 20 cases. Neurology 2004;62:932–936 Lab: Patho-physiology
    72 47d 92 Bermejo-Pareja F, Louis ED, Benito-León J. Risk of incident dementia in essential tremor: A population-based study. Mov Disord 2007;22:1573–1580 Epidemiology
    73 48 91 Louis ED, Ottman R. How familial is familial tremor? The genetic epidemiology of essential tremor. Neurology 1996;46:1200–1205 Review
    74 49a 90 Louis ED, Marder K, Cote L, et al. Differences in the prevalence of essential tremor among elderly African-Americans, whites, and Hispanics in northern Manhattan, NY. Arch Neurol 1995;52:1201–1205 Epidemiology
    75 49b 90 Findley LJ, Koller WC. Essential tremor: a review. Neurology 1987;37:1194–1197 Review
    76 49c 90 Hellwig B, Haussler S, Schelter B, et al. Tremor-correlated cortical activity in essential tremor. Lancet 2001;357:519–523 Lab: Patho-physiology
    77 50a 88 Helmchen C, Hagenow A, Miesner J, et al. Eye movement abnormalities in essential tremor may indicate cerebellar dysfunction. Brain 2003;126:1319–1332 Lab: Patho-physiology
    78 50b 88 Hallett M, Dubinsky RM. Glucose-metabolism in the brain of patients with essential tremor. J Neurol Sci 1993;114:45–48 Lab: Patho-physiology
    79 50c 88 Louis ED, Ford B, Frucht S, et al. Risk of tremor and impairment from tremor in relatives of patients with essential tremor: a community-based family study. Ann Neurol 2001;49:761–769 Epidemiology
    80 51a 87 Jeanneteau F, Funalot B, Jankovic J, et al. A functional variant of the dopamine D-3 receptor is associated with risk and age-at-onset of essential tremor. Proc Natl Acad Sci U S A 2006;103:10753–10758 Lab: Genetic studies
    81 51b 87 Jefferson D, Jenner P, Marsden CD. Beta-adrenoreceptor antagonists in essential tremor. J Neurol Neurosurg Psychiatry 1979;42:904–909 Clinical: Medicine
    82 52a 86 Benito-León J, Louis ED, Bermejo-Pareja F. Elderly-onset essential tremor is associated with dementia. Neurology 2006;66:1500–1505 Clinical: Classification
    83 52b 86 Deuschl G, Elble R. Essential tremor–neurodegenerative or nondegenerative disease towards a working definition of ET. Mov Disord 2009;24:2033–2041 Review
    84 53a 86 Shahed J, Jankovic J. Exploring the relationship between essential tremor and Parkinson’s disease. Parkinsonism Relat Disord 2007;13:67–76 Review
    85 53b 86 Leehey MA, Munhoz RP, Lang AE, et al. The fragile X premutation presenting as essential tremor. Arch Neurol 2003;60:117–121 Lab: Genetic studies
    86 54a 85 Koller W, Biary N, Cone S. Disability in essential tremor: effect of treatment. Neurology 1986;36:1001–1004 Clinical: Medicine
    87 54b 85 Deng H, Le W, Jankovic J. Genetics of essential tremor. Brain 2007;130:1456–1464 Review
    88 55a 84 Gasparini M, Bonifati V, Fabrizio E, et al. Frontal lobe dysfunction in essential tremor: a preliminary study. J Neurol 2001;248:399–402 Lab: Patho-physiology
    89 55b 84 Shill HA, Adler CH, Sabbagh MN, et al. Pathologic findings in prospectively ascertained essential tremor subjects. Neurology 2008;70:1452–1455 Lab: Patho-physiology
    90 56 83 Koller WC, Vetere-Overfield B. Acute and chronic effects of propranolol and primidone in essential tremor. Neurology 1989;39:1587–1588 Clinical: Medicine
    91 57a 82 Jain S, Lo SE, Louis ED. Common misdiagnosis of a common neurological disorder : how are we misdiagnosing essential tremor? Arch Neurol 2006;63:1100–1104 Clinical: Classification
    92 57b 82 Jankovic J. Essential tremor: a heterogeneous disorder. Mov Disord 2002;17:638–644 Clinical: Classification
    93 57c 82 Troster AI, Woods SP, Fields JA, et al. Neuropsychological deficits in essential tremor: an expression of cerebello-thalamo-cortical pathophysiology? Eur J Neurol 2002;9:143–151 Lab: Patho-physiology
    94 57d 82 Axelrad JE, Louis ED, Honig LS, et al. Reduced Purkinje cell number in essential tremor. Arch Neurol 2008;65:101–107 Lab: Patho-physiology
    95 58 81 Brin MF, Lyons KE, Doucette J, et al. A randomized, double masked, controlled trial of botulinum toxin type A in essential hand tremor. Neurology 2001;56:1523–1528 Clinical: Medicine
    96 59a 80 Wills AJ, Jenkins IH, Thompson PD, et al. A positron emission tomography study of cerebral activation-associated with essential and writing tremor. Arch Neurol 1995;52:299–305 Lab: Patho-physiology
    97 59b 80 Louis ED, Ford B, Lee H, et al. Diagnostic criteria for essential tremor: a population perspective. Arch Neurol 1998;55:823–828 Clinical: Classification
    98 59c 80 Kralic JE, Criswell HE, Osterman JL, et al. Genetic essential tremor in gamma-aminobutyric acidA receptor alpha 1 subunit knockout mice. J Clin Invest 2005;115:774–779 Lab: Genetic studies
    99 60a 79 Cleeves L, Findley LJ, Koller W. Lack of association between essential tremor and Parkinson’s disease. Ann Neurol 1988;24: 23–26 Epidemiology
    100 60b 79 Tan EK, Matsuura T, Nagamitsu S, et al. Polymorphism of NACP-Rep1 in Parkinson’s disease: An etiologic link with essential tremor? Neurology 2000;54: 1195–1198 Lab: Genetic studies

    Table 3

    Summary of Top 100 Articles on Dystonia Citations for Dystonia (Ranked in Order of Citations)

    Absolute Number Rank Citations Paper Category
    1 1 560 Ozelius LJ, Hewett JW, Page CE, et al. The early-onset torsion dystonia gene (DYT1) encodes an ATP binding protein. Nat Genet 1997;17:40–48 Lab: Genetic studies
    2 2 537 Burke RE, Fahn S, Marsden CD, et al. Validity and reliability of a rating-scale for the primary torsion dystonias. Neurology 1985;35:73–77 Clinical: Classification
    3 3 523 Ichinose H, Ohye T, Takahashi E, et al. Hereditary progressive dystonia with marked diurnal fluctuation caused by mutations in the GTP cyclohydrolase-I gene. Nat Genet 1994;8:236–242 Lab: Genetic studies
    4 4 491 Berardelli A, Rothwell JC, Hallett M, et al. The pathophysiology of primary dystonia. Brain 1998;121:1195–1212 Lab: Patho-physiology
    5 5 453 Tsui JKC, Stoessl AJ, Eisen A, et al. Double-blind-study of botulinum toxin in spasmodic torticollis. Lancet 1986;2:245–247 Clinical: Medicine
    6 6 438 Vidailhet M, Vercueil L, Houeto JL, et al. Bilateral deep-brain stimulation of the globus pallidus in primary generalized dystonia. N Engl J Med 2005;352:459–467 Clinical: Surgery
    7 7 391 Ridding MC, Sheean G, Rothwell JC, et al. Changes in the balance between motor cortical excitation and inhibition in focal, task specific dystonia. J Neurol Neurosurg Psychiatry 1995;59:493–498 Clinical: Medicine
    8 8 363 Burke RE, Fahn S, Jankovic J, et al. Tardive dystonia: late-onset and persistent dystonia caused by anti-psychotic drugs. Neurology 1982;32:1335–1346 Lab: Patho-physiology
    9 9 362 Kupsch A, Benecke R, Mueller J, et al. Pallidal deep-brain stimulation in primary generalized or segmental dystonia. N Engl J Med 2006;355:1978–1990 Clinical: Surgery
    10 10 320 Sheehy MP, Marsden, CD. Writers cramp -a focal dystonia. Brain 1982;105: 461–480 Clinical: Classification
    11 11 312 Risch N, de Leon D, Ozelius L, et al. Genetic-analysis of idiopathic torsion dystonia in Ashkenazi Jews and their recent descent from a small founder population. Nat Genet 1995;9:152–159 Lab: Genetic studies
    12 12 311 Byl NN, Merzenich MM, Jenkins WM. A primate genesis model of focal dystonia and repetitive strain injury 1. Learning-induced dedifferentiation of the representation of the hand in the primary somatosensory cortex in adult monkeys. Neurology 1996;47:508–520 Lab: Patho-physiology
    13 13 292 Vitek JL, Chockkan V, Zhang JY, et al. Neuronal activity in the basal ganglia in patients with generalized dystonia and hemiballismus. Ann Neurol 1999;46:22–35 Lab: Patho-physiology
    14 14 282 Berardelli A, Rothwell JC, Day BL, et al. Patho-physiology of blepharospasm and oromandibular dystonia. Brain 1985;108:593–608 Lab: Patho-physiology
    15 15 279 Siebner HR, Tormos JM, Ceballos-Baumann AO, et al. Low-frequency repetitive transcranial magnetic stimulation of the motor cortex in writer’s cramp. Neurology 1999;52:529–537 Clinical: Medicine
    16 16 259 Jankovic J, Orman J. Botulinum-a toxin for cranial-cervical dystonia: a double-blind, placebo-controlled study. Neurology 1987;37:616–623 Clinical: Medicine
    17 17a 255 Elbert T, Candia V, Altenmuller E, et al. Alteration of digital representations in somatosensory cortex in focal hand dystonia. Neuroreport 1998;9:3571–3575 Lab: Patho-physiology
    18 17b 255 Jankovic J, Schwartz K, Donovan DT. Botulinum toxin treatment of cranial-cervical dystonia, spasmodic dysphonia, other focal dystonias and hemifacial spasm. J Neurol Neurosurg Psychiatry 1990;53:633–639 Clinical: Medicine
    19 17c 255 Coubes P, Roubertie A, Vayssiere N, et al. Treatment of DYT1-generalised dystonia by stimulation of the internal globus pallidus. Lancet 2000;355:2220–2221 Clinical: Surgery
    20 18 248 Zimprich A, Grabowski M, Asmus F, et al. Mutations in the gene encoding epsilon-sarcoglycan cause myoclonus-dystonia syndrome. Nat Genet 2001;29:66–69 Lab: Genetic studies
    21 19 246 Brin MF, Fahn S, Moskowitz C, et al. Localized injections of botulinum toxin for the treatment of focal dystonia and hemifacial spasm. Mov Disord 1987;2:237–254 Clinical: Medicine
    22 20 242 Nutt JG, Muenter MD, Aronson A, et al. Epidemiology of focal and generalized dystonia in Rochester, Minnesota. Mov Disord 1988;3:188–194 Epidemiology
    23 21 234 Greene P, Kang U, Fahn S, et al. Double-blind, placebo-controlled trial of botulinum toxin injections for the treatment of spasmodic torticollis. Neurology 1990;40:1213–1218 Clinical: Medicine
    24 22 233 Jankovic J, Leder S, Warner D, et al. Cervical dystonia: clinical findings and associated movement-disorders. Neurology 1991;41:1088–1091 Epidemiology
    25 23 231 Greene P, Fahn S, Diamond B. Development of resistance to botulinum toxin type-a in patients with torticollis. Mov Disord 1994;9:213–217 Clinical: Medicine
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    67 57a 162 Jin H, May M, Tranebjaerg L, et al. A novel X-linked gene, DDP, shows mutations in families with deafness (DFN-1), dystonia, mental deficiency and blindness. Nat Genet 1996;14:177–180 Lab: Genetic studies
    68 57b 162 Nygaard TG, Marsden CD, Fahn S. Dopa-responsive dystonia: long-term treatment response and prognosis. Neurology 1991;41:174–181 Clinical: Medicine
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    71 58c 161 Newton MR, Berkovic SF, Austin MC, et al. Dystonia, clinical lateralization, and regional blood-flow changes in temporal-lobe seizures. Neurology 1992;42:371–377 Epidemiology
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    For further analysis of the most cited works, each article was classified into one of seven categories: epidemiology, laboratory genetic studies, laboratory pathophysiological studies, clinical classification, clinical medical therapies, clinical surgical therapies, and review articles. The numbers of articles in each category by field of study (ET and dystonia) are shown in Figure 1.

    Figure 1 

    Plot Showing the Number of Articles by Category. Essential Tremor (shaded grey) and dystonia (hatched lines).

    Epidemiology

    Studies were included in this category if they described the epidemiology of the condition including prevalence, incidence, comparisons, and trends over time. For ET, there were 15 studies in this category. Out of these, eight studies investigated the incidences of ET in different regions or countries. The remaining seven examined the association of ET with dementia, PD, and other functional measures. By comparison, there were only four dystonia articles in this category. These studies investigated the prevalence of dystonia in different population subgroups.

    Clinical: classification

    This broad category included new description of the disease, new diagnostic features, its classification into subtypes, as well as condition-specific measures and rating scales. There were 18 articles in this category, including one citation classic for ET.11 Similarly, there were 13 articles for dystonia and one citation classic.16

    Laboratory: genetic studies

    Studies were included in this category if they were genetic studies. There were seven studies for ET, including investigations in the familial essential tremor gene FET1, fragile X premutation, variants in the sequences of the LINGO1 gene and the dopamine D-3 receptor, GABA(A) alpha 1 receptor knockout, polymorphism of NACP-Rep1, and methodologic issues in ET research. For dystonia, there were 19 studies including two citation classics.14,15 These two genetic studies were the first and third most highly ranked articles by citations in the dystonia field. There were five studies on the early onset dystonia gene (DYT1),;four on idiopathic dystonia; two on the genetics of dopa-responsive dystonia; one on Leber optic atrophy and dystonia; one on lacZ transgene insertion; and one each on mutations of the deafness/dystonia peptide (DDP) gene, GTP cyclohydrolase-1 gene, epsilon sarcoglycan gene, dystonia musculorum gene, Na+/K+-ATPase alpha 3 gene, and phospholipase A2 group VI (PLA2G6) gene.

    Laboratory: pathophysiology

    Studies investigating the pathophysiologic mechanisms underlying ET and dystonia were included in this category. There were 21 studies for ET, including 10 that employed imaging techniques. There were four studies on the physiology of ET, five on pathology, and the remaining studies on pharmacology or biochemical analysis of cerebrospinal fluid. For dystonia, there were 20 studies with 13 on neurophysiology, six on imaging, and one on pharmacology.

    Clinical: medical therapies

    Only those studies dealing with the application of medical and nonsurgical treatments were included in this category. For ET, there were eight articles on medical treatment with two studies on propranolol and primidone, and one study each on gabapentin and propranolol, on propranolol alone, on alcohol, on botulinum toxin, and on mechanical displacement. For dystonia, there were 30 articles including one citation classic.18 The effect of botulinum toxin was investigated in 19 out of the 30 articles. The remaining articles included five studies on transcranial magnetic stimulation; three studies on levodopa; and one study each on baclofen, lidocaine, and anticholinergic treatment.

    Clinical: surgical therapies

    Only those studies that dealt primarily with surgical treatment were included in this category. In several studies, the primary aim of the surgical treatment was for tremor whose etiology could either be due to PD or ET; these were also included. For ET, there were 16 articles with three citation classics.10,12,13 There was one article on the effect of thalamotomy and two articles comparing thalamotomy with deep brain stimulation (DBS); the 13 remaining articles investigated the effects of thalamic stimulation of the ventral intermediate nucleus. For dystonia, there were nine articles on surgical therapies, all of which were studies of globus pallidus internus (GPi) DBS.

    Review articles

    There were 15 review articles for ET: seven on the general aspects of ET and the remainder reviewing the treatment, pathophysiology, and effect of electrical stimulation. For dystonia, there were five reviews of pathophysiology or diagnostic features.

    Time trends and journals

    The publication year of the most cited articles are summarized in Figure 2. This showed that there was a peak of the most cited articles for ET for articles published between 2000 and 2004, and for dystonia between 1995 and 1999. The most cited articles were published in 38 journals. The top 10 journals by numbers of articles published and numbers of citations per articles are shown in Figure 3. The top 10 journals accounted for 162 (81%) of the combined 200 most cited articles.

    Figure 2 

    Number of Most Cited Articles in 5-Year Time Periods.
    Figure 3 

    Top 10 Journals with the Highest Numbers of Most Cited Articles for Essential Tremor and Dystonia. The size of the bubble represents the 5-year journal impact factor for 2015.

    Discussion

    The most highly cited articles in the fields of ET and dystonia were identified (Tables 2 and 3). By category, the most cited studies were those on pathophysiology followed by medical treatments, clinical classification, genetic studies, surgical treatments, review articles, and epidemiology studies.

    Comparing ET and dystonia, there are very similar proportions of articles in the most cited on pathophysiology and clinical classification categories. Nevertheless, the two fields diverge in other subfields because ET is characterized by a larger number of studies describing the epidemiology of the condition, whereas dystonia has a much higher representation of genetic studies. This is likely an indication of the greater understanding and contribution of genetic factors to dystonia compared to ET, which is—by contrast—a much more common condition but probably characterized by a wide spectrum of possible etiologies, making genetic studies very difficult. Moreover, there is a predominance of surgical treatment for ET, whereas medical treatment predominates for dystonia.

    Trends over time showed that the peak period of when the most cited papers were published was between 1995 and 2005, with dystonia peaking 5 years before ET. This is in line with our previous work looking at the most cited papers in the functional neurosurgery literature, which showed a similar peak in the 1990s.6 The proposed reasons for the peak during this time are likely similar, namely that this period was particular active and productive with significant success in elucidating the causes and diagnosis of these conditions, and effective treatments such as deep brain stimulation or botulinum toxin were developed for dystonia. Another possible reason for the proposed peak may be a fundamental feature of contemporary research whereby older publications are no longer cited because they have been replaced by new studies that have replicated the findings and superseded them.6 At the same time, more recent studies have not had time to become established as a most cited article, for example the more recent discovery of the DYT6 gene.20

    The majority of the most cited articles were generally published in specialized journals such as Neurology, Annals of Neurology, Movement Disorders, Brain, Journal of Neurology, Neurosurgery, and Psychiatry, among others (Figure 3). However, articles published in the more general medical journals such as the New England Journal of Medicine or Lancet tend to receive more citations per article published. This also corresponded to their higher overall journal impact factor (Figure 3). An exception were articles published in the Journal of Neurosurgery, which received on average 356 citations per articles, more than would be expected by the journal’s impact factor. These were attributable to contributions from three studies on deep brain stimulation.12,21,22 This suggests that the publication of important clinical therapeutic studies in a specialized journal is also able to achieve significant impact.

    Limitations

    The choice of ISI Web of Science, which indexes over 15,000 journals, over Google Scholar, which indexes a wider range of academic documents may also have had an effect on our findings. However, our previous reviews in other fields yielded very similar results using these two search engines when the study field was small.6,9 Another limitation is that the search terms may not have yielded all possible results despite our inclusion of broad terms. For the ISI Web of Science search engine, it is possible to perform either a title- or topic-based search. The former would only search for the search term in the title of the article, whereas a topic-based search would also include the abstract. Given the small size of the ET and dystonia fields, a topic-based search was selected to retrieve all possible results as described in the methods section. This is particularly important for ET, as many of the studies would also include patients with parkinsonian tremor. By contrast, a citation analysis study on ET using a title-based search would yield fewer results.8 Finally, the list of most cited papers changes with time and is therefore a snapshot of the current state of research.

    Conclusions

    We performed an analysis to identify the most cited ET and dystonia papers. There are fewer citation classics compared to PD, confirming that this is a smaller field of research. Compared to dystonia, areas of research in ET such as genetics, neurophysiology, and medical treatment are underrepresented. The peak of citations for ET is also lagging by about 5 years. These findings suggest that further work remains to be carried out to improve our understanding of the basic science of ET.

    Notes

    1 Acknowledgements: None. 

    2 Financial Disclosures: None. 

    3 Conflicts of interest: Dr. King has no conflicts of interest, including relevant financial interests, activities, relationships, and affiliations. 

    4 Dr. Fasano has given expert testimony for Medtronic, has received honoraria from serving scientific board of Abbvie, Boston Scientific, and UCB pharma and has received honoraria from TEVA, UCB pharma, Medtronic, Abbvie, Boston Scientific, Novartis, and Chiesi Farmaceutici. 

    5 Dr. Lozano receives consulting fees from Medtronic, Boston Scientific, St. Jude, and Ely Lilly and holds an interest in Functional Neuromodulation. 

    6 Ethics Statement: Not applicable for this Review. 

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