Abstract

A task force of the International Parkinson and Movement Disorder Society (MDS) recently published a tremor classification scheme that is based on the nosologic principle of two primary axes for classifying an illness: clinical manifestations (Axis 1) and etiology (Axis 2). An Axis 1 clinical syndrome is a recurring group of clinical symptoms, signs (physical findings), and possibly laboratory results that suggests the presence of at least one underlying Axis 2 etiology. Syndromes must be defined and used consistently to be of value in finding specific etiologies and effective treatments. The MDS task force concluded that essential tremor is a common neurological syndrome that has never been defined consistently by clinicians and researchers. The MDS task force defined essential tremor as a syndrome of bilateral upper limb action tremor of at least 3 years duration, with or without tremor in other locations (e.g., head, voice, or lower limbs), in the absence of other neurological signs (e.g., dystonia, parkinsonism, myoclonus, ataxia, peripheral neuropathy, and cognitive impairment). Deviations from this definition should not be labeled as essential tremor. Patients with additional questionably-abnormal signs or with signs of uncertain relevance to tremor are classified as essential tremor plus. The MDS classification scheme encourages a thorough unbiased phenotyping of patients with tremor, with no assumptions of etiology, pathology, pathophysiology, or relationship to other neurological disorders. The etiologies, pathology, and clinical course of essential tremor are too heterogeneous for this syndrome to be viewed as a disease or a family of diseases.

Highlights

  • An international task force on tremor was convened by the International Parkinson and Movement Disorder Society (MDS) in 2011 to review the 1998 MDS consensus statement on tremor, which was devoted to the classification of pathologic tremors [1]

  • Retrospective reviews of outpatient clinical cohorts have shown that 40% or more of patients previously diagnosed as essential tremor (ET) are reclassified as ET plus or a combined tremor syndrome when the new MDS classification scheme is applied [23,24,25]

  • It is possible that the current definition of ET is too broad to identify etiologies and effective treatments

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Summary

INTRODUCTION

An international task force on tremor was convened by the International Parkinson and Movement Disorder Society (MDS) in 2011 to review the 1998 MDS consensus statement on tremor, which was devoted to the classification of pathologic tremors [1]. The Task Force found that the 1998 consensus did not use a consistent approach to tremor classification. The Task Force was concerned that essential tremor (ET) was often viewed as a specific disease, rather than a clinical syndrome, and that ET was not defined and diagnosed consistently in the clinic or in research. The revised classification scheme is based on the nosologic principle of two primary axes for classifying an illness: clinical manifestations (Axis 1) and etiology (Axis 2) [3]. The clinical manifestations in Axis 1 include symptoms, signs, and laboratory results that characterize the tremor disorder

ESSENTIAL TREMOR IS A SYNDROME
THE VALUE OF CLINICAL SYNDROMES
THE LIMITATIONS OF CLINICAL SYNDROMES
ETIOLOGIES OF THE ESSENTIAL TREMOR SYNDROME
PATHOPHYSIOLOGY OF ESSENTIAL TREMOR SYNDROME
Findings
SUBTYPES OF THE ESSENTIAL TREMOR SYNDROME

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