Dystonia Classification & Definition

Dystonia is defined as 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.

Improved definition and classification of dystonia

In 2013, a panel of experts from the International Parkinson and Movement Disorder Society  provided a new definition and classification of dystonia.

According to the new definition, “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 major novelty of the new definition was to recognize that tremor can be a clinical manifestation of dystonia. Indeed, many patients may experience tremor in body parts affected by dystonia (i.e. in cervical dystonia). Also, people with dystonia may also experience tremor in other body districts, for example upper limbs.  

The main aim of the new classification is to improve clinical characteristics of dystonia and organize current knowledge regarding etiology. Two axes were developed: Axis 1 for clinical characteristics and Axis 2 for aetiology. Additionally, the term “primary” and “secondary” dystonia is no longer in use and  have been replaced by the terms idiopathic dystonia (no known cause for dystonia), “inherited” (dystonia due to a genetic mutation) and  “acquired” dystonia. Also, this classification has introduced the term “Isolated dystonia” which refers to people having only dystonia and no other movement disorder or neurological signs. “Combined dystonia” refers to people having dystonia associated to other movement disorders. For example, lower limb dystonia in people with Parkinson’s disease is a “combined dystonia”. 

Axis 1 – Clinical characteristic:

  1. Age of onset

Infancy (birth to 2 years)

Childhood (3–12 years)

Adolescence (13–20 years)

Early adulthood (21–40 years)

Late adulthood (>40 years)

  1. Body distribution

FOCAL – Only one body region is affected (e.g. blepharospasm, oromandibular dystonia, cervical dystonia, laryngeal dystonia, and writer’s cramp).

SEGMENTAL – Two or more contiguous body regions are affected( e.g. cranial dystonia)

MULTIFOCAL – Two noncontiguous or more body regions are involved.

GENERALIZED – The trunk and at least 2 other sites are involved.

HEMIDYSTONIA – More body regions restricted to one body side are involved (e.g. brain lesions)

  1. Temporal pattern ( e.g. Disease course and Variability)
  2. Associated features (isolated dystonia or combined with another movement disorder)

Axis 2 – Aetiology

  1. Nervous system pathology (neurodegeneration/structural  lesion/ No evidence of degeneration or structural lesion)
  2. Inherited or acquired
  3. Idiopathic (sporadic/familial)