|Year : 2018 | Volume
| Issue : 7 | Page : 12--14
Classification of movement disorders: The problem of terminology
Department of Neurology, Govind Ballabh Pant Postgraduate Institute of Medical Education and Research, New Delhi, India
Dr. Sanjay Pandey
Department of Neurology, Academic block, Room No 507, Department of Neurology, Govind Ballabh Pant Postgraduate Institute of Medical Education and Research; New Delhi - 110 002
|How to cite this article:|
Pandey S. Classification of movement disorders: The problem of terminology.Neurol India 2018;66:12-14
|How to cite this URL:|
Pandey S. Classification of movement disorders: The problem of terminology. Neurol India [serial online] 2018 [cited 2021 Jun 12 ];66:12-14
Available from: https://www.neurologyindia.com/text.asp?2018/66/7/12/226446
The term 'movement disorder' came into existence in 1968, when Stanley Fahn established the first movement disorder clinic at the University of Pennsylvania. Before that, the term 'extrapyramidal disorders' was used, which was originally coined by Wilson to describe neurological ailments secondary to disorders of the basal ganglia and its pathways. However, this term was not widely acceptable considering the intimate connections of basal ganglia with pyramidal tract; and, some movement disorders, such as myoclonus and ataxia were not associated with a basal ganglia pathology. Jorg Baumann attempted the first formal classification of extrapyramidal disorders in 1963, which was based on anatomic localization of the pathology. Fahn, Marsden and Jankovic first classified the movement disorders in two groups, as hypokinetic (paucity of movements) and hyperkinetic (excess movements). The most distinguishing feature of hypokinetic movement disorders is bradykinesia, typically present in Parkinson's disease and other parkinsonian disorders. Hyperkinetic movement disorders are subdivided into tremors, dystonia, athetosis, chorea, ballism, tics, stereotypy and akathisia. Gait disorder, ataxia, hemifacial spasm and spasticity are often also included in movement disorders. A group of movement disorders with a different phenomenology caused by underlying psychological factors are referred to as psychogenic or functional movement disorders.
Appearance of new etiologies and a better knowledge of the phenomenology, pathology and genetics have highlighted the inherent shortcomings of the current classification of movement disorders. In the following sections, dystonia and tremor will be used to illustrate the clinical and pathological heterogeneity, where new classifications have been recently published.,
Oppenheim coined the term 'dystonia' in 1911, when he described 4 patients. He called the manifestation 'dystonia musculorum deformans', which today is known as primary generalized torsion dystonia. In 1984, Dystonia Medical Research Foundation provided the first definition of dystonia as a syndrome consisting “of sustained muscle contractions, frequently causing twisting and repetitive movements, or abnormal postures.” They recommended a classification that included the age at onset of the disease, bodily distribution, and etiology. Later Fahn, Bressman and Marsden added a new etiological category, 'dystonia-plus' in an attempt to separate non-degenerative dystonias from primary dystonias.
To increase the ease of clinical practice in terms of recognition, management and treatment of the disease and also to aid in further clinical and scientific research, an international consensus committee was formed in 2012, which forwarded the following revised definition to incorporate the entire spectrum of dystonia:
“Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both. Dystonic movements are typically patterned, twisting, and may be tremulous. Dystonia is often initiated or worsened by voluntary action and associated with overflow muscle activation.” The definition includes region-specific as well as task-specific dystonias and also includes the different phenomenology associated with the disease while excluding pseudo-dystonias and mimickers. The consensus committee also restructured the axes of the classification from the previously accepted three parameters (etiology, age at onset of the disease and body distribution) to two distinct axes (clinical characteristics and etiology).
The clinical characteristics included under axis 1 are age at onset of the disease (infancy, childhood, adolescence, early adulthood, and late adulthood), body distribution (focal, segmental, multifocal, hemi-dystonia, and generalized), temporal pattern (course and variability), and associated features (whether isolated or combined or with any neurological or systemic manifestations). Use of this axis helps to recognise dystonia syndromes and assemble them into useful phenomenological categories (early-onset generalized isolated dystonia, focal or segmental isolated dystonia with onset in adulthood, dystonia–parkinsonism and myoclonus dystonia). The axis 2 addresses the etiology of dystonia. Instead of using the terms 'primary' or 'secondary', the new classification distinguishes the various types of dystonia on the basis of the nervous system pathology (inherited, acquired, and idiopathic) that is responsible for the movement disorder.
The new classification is able to resolve several inconsistencies existing in the previous terminology, but some issues were resolved only in part. Better differentiation methods are still required to define pseudo-dystonia and psychogenic dystonia. Another limitation of the new classification is the lack of consideration of the microscopic changes (cell loss and degeneration) prevalent in the brain tissues.
Tremor is the oldest described movement disorder discussed in Bible, Sanskrit and ancient Greek literature (shaking caused by great fear). The classification of tremor has varied, and most have been based on anatomy, physiology, etiology and phenomenology. In 1853, Romberg classified tremors based on etiology (alcohol, mercury, paralysis agitans and senile tremor fever). Subsequently, several classifications to describe the types of tremors were proposed by many authors, including Gowers (1893), Oppenhelm (1911), Wilson (1940), and Jankovic and Fahn (1980). In 1998, an ad hoc scientific committee of the Movement Disorder Society on Tremor published a consensus statement on the terminology and classification of tremors based on the phenomenology and syndromic approach. The phenomenology-based approach broadly classified tremor as 'rest' and 'action' tremors. Action tremor was further classified as postural, kinetic, task-specific and isometric. The syndromic approach classified tremor as physiologic tremor, enhanced physiologic tremor, essential tremor, dystonic tremor syndromes, parkinsonian tremor syndrome, cerebellar tremor syndromes, Holmes' tremor, palatal tremor syndrome, drug-induced and toxic tremor syndromes, tremor syndromes in peripheral neuropathy, psychogenic tremor and unclassified tremor. One of the major limitations of the 1998 criterion is in not using a consistent approach to tremor classification. In some instances, a tremor was defined according to its anatomical origin (e.g., cerebellar tremor presenting as intention tremor); and at other instances, tremor was defined according to its etiology (e.g., tremor associated with neuropathies). Another problem was highlighted by the phenotypic variability and associated signs and symptoms in patients diagnosed with essential tremor. To facilitate a deeper understanding and consensual phenotyping of patients suffering from essential tremor and other forms of tremor, another consensus statement on the classification of tremor has been published in 2017 by the Task Force on Tremor of the International Parkinson and Movement Disorder Society. This task force has defined tremor as “an involuntary, rhythmic, oscillatory movement of a body part.” The task force proposed tremor classification based on two main axes: Clinical features (axis I) and etiology (axis II). The axis 1 consisting of clinical features of tremor is specified in terms of medical history (age at onset, past medical history, family history, alcohol and drug history and temporal evolution), tremor characteristics (body distribution, tremor frequency and activation conditions), and associated signs (signs of systemic illness, neurologic signs and soft signs). For some patients, additional laboratory tests (electrophysiology, imaging and biomarkers) may be required. The axis 2, which is the etiological classification, classifies the types of tremors as belonging to the genetic, acquired or idiopathic etiology. The new tremor classification provides the much-needed improvement that was required in the old classification. All tremor types are well classified. There are, however, some limitations also in the present classification, which are best highlighted by the definition of essential tremor. Expressions such as “questionable dystonic posturing” in the diagnosis of 'essential tremor plus' state, indicates the uncertainty prevalent in the diagnosis.,, The minimal requirements for diagnosing dystonia in each body part are still undefined.,
The dystonia and tremor classifications highlight the inherent shortcomings in the current classification of movement disorders, which are due to the complex nature of the phenomenology and the lack of diagnostic tests for the majority of these ailments. This has been further complicated by the newly emerging genetic and molecular information. It may not be possible to provide the ultimate classification. Continued research by both clinicians and researchers is, therefore, required to refine and redefine classifications of movement disorders.
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