Do We Belittle Essential Tremor by Calling It a Syndrome Rather Than a Disease? No

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.

Essential Tremor

“…However, this syndrome vs disease issue is controversial, and it is discussed in detail elsewhere. 12,13 A wide variety of conditions, that is, neurodegenerative, genetic, metabolic, toxin and drug exposures, infections, and structural brain lesions, may result in tremor, and such underlying conditions should be ruled out before labeling the tremor as ET. 1 The conditions that may present with isolated action tremor resembling that in ET are DT, SCA12, and DYT 24 (ANO3 variation).…”

Phenotypic Features of Isolated Essential Tremor, Essential Tremor Plus, and Essential Tremor-Parkinson’s Disease in a Movement Disorders Clinic

“…Essential tremor was defined as an Axis 1 tremor syndrome with “isolated tremor syndrome of bilateral upper limb action tremor” of “at least 3 years’ duration” in the “absence of other neurological signs, such as dystonia, ataxia, or parkinsonism”. “Essential tremor plus” was adopted to describe tremor with the characteristics of ET as well as “additional neurological signs of uncertain significance” [ 1 ], in order to accommodate the additional movement disorders and non-motor symptoms increasingly described in ET patients [ 2 3 4 5 6 7 8 ].…”

“…These Axis 1 definitions, based on clinical features, and the division into isolated ET and ET plus have been challenged and have created controversy within the field [ 4 9 10 11 12 ]. Some studies have found that a majority of patients with a prior diagnosis of ET require reclassification from ET to ET plus [ 9 10 ].…”

Cutaneous alpha‐synuclein deposition in postural tachycardia patients

“…The diagnostic approach and conclusions that underlie the present manuscript are consonant with classical illness nosological principles, that is, syndromes such as POTS, Sjogren's syndrome, Tourette's syndrome, and essential tremor, for example, are defined as a recurring group of clinical symptoms, signs, and test results without a known etiology. [51][52][53] Inherent to these principles is that a defined syndrome is a waystation 51 -a "diagnostic placeholder"-on the scientific journey toward the discovery of specific etiologies and treatment. Thus, the diagnostic approach and identification of cutaneous alpha-synuclein in these patients could be considered a step toward the delineation of an etiology in a small subgroup of the heterogeneous postural tachycardia syndrome population.…”