Dystonia

Dystonia is a neurological hyperkinetic movement disorder characterised by involuntary, sustained or repetitive muscle contractions that lead to twisting and abnormal postures. These movements often resemble tremors and can be exacerbated by physical activity.

The disorder can progress, affecting adjacent muscles, and can be either hereditary or caused by factors such as birth trauma, head injury, infection, toxins, or medication.

Classification

Dystonia is classified based on clinical characteristics and causes. Clinical characteristics include age of onset, body distribution, nature of symptoms, and associated features like additional movement disorders or neurological symptoms. Causes can include changes or damage to the nervous system and inheritance patterns.

Types

• Generalised Dystonias: For example, dystonia musculorum deformans, which starts in the lower limbs and spreads upwards, is autosomal dominant, and has a childhood onset.
• Focal Dystonias: These include:
  • Anismus: Affects rectal muscles causing painful defecation.
  • Cervical Dystonia: Affects neck muscles causing the head to rotate or pull in various directions.
  • Blepharospasm: Involves muscles around the eyes, leading to rapid blinking or forced closure.
  • Oculogyric Crisis: Affects eye and head muscles, often induced by medications.
  • Oromandibular Dystonia: Involves jaw and tongue muscles causing distortions.
  • Spasmodic Dysphonia: Affects laryngeal muscles, altering the voice.
  • Focal Hand Dystonia: Affects hand muscles, interfering with activities like writing or playing instruments.

Signs and Symptoms

Symptoms vary widely but often include abnormal posturing, continuous pain, cramping, and relentless muscle spasms. Diagnosis can be challenging due to symptom overlap with other disorders like Parkinson's disease, essential tremor, and Tourette's syndrome. Dystonia is prevalent in individuals with Huntington's disease, particularly those with long disease durations and on antidopaminergic medications.

Causes

Primary dystonia is suspected when no identifiable cause or structural CNS abnormality is present. It is believed to originate in brain areas concerned with motor function, like the basal ganglia. Infections like meningitis and encephalitis, or malfunction of the sodium-potassium pump, can also cause dystonia. Emerging evidence suggests cerebellar involvement in the disease's pathophysiology.

Diagnosis

Diagnostic methods include genetic testing, electromyography, blood tests, MRI, or CT scans to rule out other conditions and identify potential genetic or structural causes.

Treatment

Treatment is highly individualised and may include medication, physical therapy, botulinum toxin injections, and surgical procedures like deep brain stimulation (DBS).

Medication

Anticholinergics and dopamine agonists are commonly used. Clonazepam, a benzodiazepine, is also prescribed but has limited effects and notable side effects.

Physical Intervention

Physical therapy can manage balance, mobility, and overall function. Techniques include splinting, therapeutic exercise, postural training, and gait training. Sensorimotor retraining activities show promise in inducing neuroplasticity, aiding recovery in cases like cervical dystonia and focal hand dystonia.

Botulinum Toxin Injection

Botulinum toxin injections provide relief for 3–6 months. The injections must be repeated, and around 15% of recipients may develop immunity to the toxin.

Surgery

Surgical options include selective denervation and DBS, which has been successful in severe generalised dystonia cases. However, DBS may increase the risk of suicide in medication-refractory dystonia patients.

History

The Italian Bernardino Ramazzini first described task-specific dystonia in 1713. Detailed descriptions emerged in 1911, and dystonia's classification was expanded in the 1970s to include focal and segmental cases. The modern definition and classification schemes were established in the 1980s, recognising the disorder's clinical complexity.

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Self-assessment MCQs (single best answer)

What is dystonia characterised by?

Which of the following is a type of generalised dystonia?

What is the typical onset age for dystonia musculorum deformans?

Which muscle group is primarily affected by anismus?

Which diagnostic method is NOT typically used to diagnose dystonia?

Which medication is commonly used in the treatment of dystonia?

What is the effect duration of botulinum toxin injections for dystonia?

Which surgical procedure is used for severe generalised dystonia?

What increased risk is associated with DBS in medication-refractory dystonia patients?

Who first described task-specific dystonia?