What is dystonia?

Dystonia: Definition, Classification, and Management

Dystonia is defined as a neurological movement disorder characterized by involuntary sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both. 1, 2 These movements are typically patterned and twisting, and may be tremulous. Dystonia is often initiated or worsened by voluntary action and associated with overflow muscle activation.

Clinical Characteristics of Dystonia

Key Features

• Involuntary sustained muscle contractions
• Twisting or squeezing movements and abnormal postures
• Movements can be stereotyped and repetitive
• Speed varies from rapid to slow
• Sustained contractions can result in fixed postures 3

Common Patterns and Modifying Factors

• Often worsens with:
  • Anxiety
  • Heightened emotions
  • Fatigue
• Often improves with:
  • Relaxation
  • Sleep (disappears during sleep)
  • Sensory tricks ("gestes antagonistes") - specific sensory stimuli that temporarily reduce dystonia 3
• May show diurnal fluctuations (minimal symptoms in morning, worsening throughout day)
• May occur in relation to specific voluntary actions

Classification of Dystonia

Dystonia is classified along two primary axes 2:

1. Clinical Characteristics

• Age at onset: Infancy, childhood, adolescence, early adulthood, late adulthood
• Body distribution:
  • Focal (single body region)
  • Segmental (contiguous body regions)
  • Multifocal (non-contiguous body regions)
  • Generalized (trunk plus at least two other body regions)
  • Hemidystonia (half of the body)
• Temporal pattern:
  • Persistent
  • Action-specific
  • Diurnal
  • Paroxysmal
• Associated features:
  • Isolated dystonia (dystonia is the only motor feature)
  • Combined dystonia (dystonia with other movement disorders)

2. Etiology

• Nervous system pathology:
  • Evidence of degeneration
  • Evidence of structural lesions
  • No evidence of degeneration or structural lesion
• Inheritance:
  • Inherited (autosomal dominant, autosomal recessive, X-linked, mitochondrial)
  • Acquired (brain injury, infection, drug-induced, toxic, vascular, neoplastic)
  • Idiopathic (sporadic, familial)

Common Types of Dystonia

Focal Dystonias

• Cranial dystonia: Includes blepharospasm, oromandibular dystonia, lingual dystonia, and spasmodic dysphonia
• Cervical dystonia (spasmodic torticollis): Abnormal head and neck postures
• Writer's cramp: Task-specific dystonia affecting the hand during writing 3
• Paroxysmal kinesigenic dyskinesia (PKD): Characterized by sudden attacks triggered by voluntary movements 4

Genetic Forms

Several genes have been identified in dystonia, including:

• TOR1A, THAP1, GCH1, KMT2B (isolated or combined dystonia)
• PRRT2 (most common cause of paroxysmal kinesigenic dyskinesia) 4, 5, 6

Diagnosis of Dystonia

Diagnosis is primarily clinical and based on characteristic features:

Key Diagnostic Features

• Sustained or intermittent muscle contractions
• Abnormal postures or movements
• Patterned, twisting movements
• Action-induced or task-specific symptoms
• Sensory tricks that temporarily relieve symptoms

Red Flags Suggesting Secondary Causes 4

• Duration of attacks >1 minute
• Age of onset over 20 years
• Abnormalities on brain imaging
• No response to appropriate medications
• Abnormal interictal examinations

Differential Diagnosis 7

Dystonia may be confused with:

• Tremor
• Parkinson's disease
• Myoclonus
• Chorea
• Tics
• Psychogenic movement disorders

Treatment Options

First-Line Treatments

• Botulinum toxin injections: First-line for focal and segmental dystonia, providing symptom control for 3-6 months with approximately 73% improvement rate 1
• Anticholinergics (e.g., trihexyphenidyl): Particularly effective for medication-induced dystonia and in pediatric patients 1
• Sodium channel blockers (carbamazepine/oxcarbazepine): Effective for paroxysmal forms of dystonia, especially PKD 4, 1

Second-Line Treatments

• Benzodiazepines: When trihexyphenidyl is ineffective or poorly tolerated 1
• Deep brain stimulation: For medication-refractory dystonia, particularly primary generalized or cervical dystonia, targeting the Globus Pallidus Interna (GPi) 1

Special Considerations

• Medication-induced dystonia: Discontinue the offending agent when possible; acute dystonic reactions require immediate treatment with anticholinergics (benztropine) or antihistamines (diphenhydramine) 1
• Age-specific responses: Pediatric patients often respond better to anticholinergics than adults, while elderly patients require lower doses due to increased side effect risk 1

Management Strategies

Supportive Care

• Maintain optimal postural alignment
• Implement graded activity to normalize movement patterns
• Develop strategies to reduce muscle overactivity, pain, and fatigue 1

For Voice-Related Dystonia

• Adequate hydration
• Voice rest when needed
• Use amplification in large spaces
• Indoor air humidification in dry environments
• Avoid smoking, excessive throat clearing, and drying medications 1

Dystonia remains a complex disorder with varied presentations and causes. Early recognition and appropriate treatment can significantly improve quality of life for affected individuals.