What is Dystonia
Dystonia is a neurological syndrome characterized by involuntary, sustained muscle contractions that produce twisting, repetitive movements and abnormal postures due to co-contraction of agonist and antagonist muscles. 1, 2
Core Clinical Features
Dystonia manifests as stereotyped, patterned muscle contractions that cause the affected body part to twist into abnormal positions, with movements that can range from rapid to slow, and sustained contractions that may result in fixed postures 2, 3. The International Parkinson and Movement Disorder Society recognizes that dystonia can present as pure dystonic movements, chorea, ballism, or mixed forms 1.
Key Distinguishing Characteristics
- Stereotypy: The pattern of abnormal posture or movement remains constant in the short term, even when severity fluctuates, which helps differentiate dystonia from psychogenic reactions 4
- Task specificity: Dystonia may appear only during specific voluntary actions (such as writing in writer's cramp), particularly in early phases 2, 4
- Sensory tricks (geste antagoniste): Patients often discover that light touch or specific sensory stimuli temporarily reduce dystonic movements, such as touching the chin lightly in cervical dystonia 2, 4
- Overflow phenomenon: Unnecessary muscle activation occurs during voluntary tasks, with dystonia spreading to adjacent body regions 4
- Morning benefit: Symptoms are typically milder in the morning with worsening throughout the day, though this varies among individuals 2, 4
- Disappearance during sleep: Dystonic movements characteristically resolve during sleep and worsen with anxiety, heightened emotions, and fatigue 2
Classification by Distribution
The American Academy of Neurology classifies dystonia by anatomical distribution 1:
- Focal: Single body region (e.g., blepharospasm, cervical dystonia, writer's cramp)
- Segmental: Two or more contiguous body regions
- Multifocal: Two or more non-contiguous regions
- Generalized: Trunk plus at least two other sites
Etiological Categories
Primary (Isolated) Dystonia
Primary genetic forms are the most common cause of isolated dystonia, where dystonia and tremor are the sole neurological features without other systemic or neurological symptoms 1, 2. Genetic dystonias can be inherited in autosomal dominant patterns with incomplete penetrance of 60-90% 1.
Combined Dystonia
Combined dystonia presents with additional neurological symptoms including benign familial infantile epilepsy, febrile convulsions, migraine or hemiplegic migraine, episodic ataxia, developmental delay, intellectual deficit, language dysfunction, and autism 1.
Secondary Dystonia
Secondary causes must be systematically excluded through appropriate workup 5:
- Medication-induced: First-generation antipsychotics are the most common culprit, with acute dystonia occurring within the first few doses or after dose increases 1, 6. Risk factors include young age, male gender, and high-potency dopamine D2 receptor antagonists 6
- Metabolic disorders: Hyperthyroidism, calcium-phosphate metabolism disorders (hypoparathyroidism, pseudoparathyroidism), glucose metabolism disorders, and kernicterus 5, 1
- Neurological diseases: Wilson's disease (copper accumulation), Parkinson's disease, cerebrovascular disease/stroke 1
- Structural causes: Brain trauma, demyelinating disease (especially multiple sclerosis) 5, 1
Epidemiology
Dystonia is the third most common movement disorder in humans, following essential tremor and Parkinson's disease 3, 7.
Common Pitfalls in Diagnosis
- Do not confuse with tardive dyskinesia: Unlike some forms of paroxysmal kinesigenic dyskinesia where patients can attenuate attacks by slowing movements when experiencing an aura, tardive dyskinesia has no voluntary control component 8
- Recognize "negative dystonia": This controversial concept includes non-paretic loss of muscle activation necessary for tasks, manifesting as apraxia of lid opening/closure, dropped head syndrome, camptocormia, or Pisa syndrome 4
- Distinguish from psychogenic movements: The stereotyped, consistent pattern of dystonia over time helps differentiate it from functional/psychogenic disorders 4
Pathophysiology
The underlying mechanism involves loss of reciprocal inhibition of muscle activities, causing involuntary simultaneous contractions of agonist and antagonist muscles (co-contraction), with excessive recruitment in affected muscles 1, 4.