Table 1.

Classification of dystonia, based on the European Federation of Neurological Societies current scheme

By aetiology
1. Primary dystonia
1.1 Primary pure dystonia	Torsion dystonia is the only clinical sign (apart from tremor) and there is no identifiable exogenous cause or other inherited or degenerative disease
1.2 Primary plus dystonia	Torsion dystonia is a prominent sign but is associated with another movement disorder, for example myoclonus or parkinsonism. There is no evidence of neurodegeneration.
1.3 Primary paroxysmal dystonia	Torsion dystonia occurs in brief episodes with normalcy in between. Three main forms are known depending on the triggering factor.
2. Heredodegenerative dystonia	Dystonia is a feature, among other neurological signs, of a heredodegenerative disorder, such as Wilson's disease
3. Secondary dystonia	Dystonia is a symptom of an identified neurological condition, such as a focal brain lesion, exposure to drugs or chemicals, e.g. dystonia because of a brain tumour, off-period dystonia in Parkinson's disease.
By age at onset
1. Early onset (<30 years of age)	Usually starts in a leg or arm and frequently progresses to involve other limbs and the trunk
2. Late onset	Usually starts in the neck (including the larynx), the cranial muscles or one arm. Tends to remain localized with restricted progression to adjacent muscles
By distribution of affected body parts
1. Focal	Single body region (e.g. writer’s cramp, blepharospasm)
2. Segmental	Contiguous body regions (e.g. cranial and cervical, cervical and upper limb)
3. Multifocal	Non-contiguous body regions (e.g. upper and lower limb, cranial and upper limb)
4. Generalized	Both legs and at least one other body region (usually one or both arms)
5. Hemidystonia	Half of the body (usually secondary to a lesion in the contralateral basal ganglia)