Dystonias

Definition/diagnostic criteria Dystonias are a group of neurological disorders characterised by involuntary muscle contractions, causing repetitive movements or abnormal postures. Dystonias are classified by their clinical characteristics, such as age of onset, body distribution, temporal pattern, and associated features (e.g. neurological or systemic).

Epidemiology Dystonia is one of the most common movement disorders. In the UK, the prevalence is estimated to be approximately 30 cases per 100,000 in the general population. Some early-onset forms have a genetic aetiology. The prevalence of dystonia varies with age, being more common in middle-aged and older adults, particularly for focal dystonias. Antipsychotics and antiemetics can trigger or worsen dystonias.

Diagnosis
Clinical features: The diagnosis of dystonia is primarily clinical, based on observation of characteristic movements and postures. Common presentations include cervical dystonia (neck), blepharospasm (eyelids), and writer’s cramp (hand). Early-onset dystonias often start in a limb and may generalise, while late-onset dystonias tend to remain focal or segmental. Non-motor symptoms, including pain and psychiatric comorbidities, are also common.

Investigations: There are no specific diagnostic tests for dystonia. However, investigations are important to exclude secondary causes. These may include MRI to rule out structural brain abnormalities, and blood tests for metabolic or genetic disorders. Electromyography (EMG) can aid in confirming the diagnosis and differentiating from other movement disorders.

Treatment The treatment of dystonia is symptomatic and tailored to the individual. Botulinum toxin injections are the first-line treatment for focal dystonias like cervical dystonia and blepharospasm. Oral medications, such as anticholinergics (e.g., trihexyphenidyl) or baclofen may be used, particularly in generalised or segmental dystonia. Deep brain stimulation (DBS) is an option for severe, treatment-resistant cases. Physiotherapy and occupational therapy play a supportive role in managing disability.

Prognosis The prognosis of dystonia varies widely depending on the type and severity. Focal dystonias, while often chronic, do not typically affect life expectancy and can be effectively managed with treatments like botulinum toxin. Generalised dystonias, especially those with early onset, may be more disabling and less responsive to treatment. Psychosocial support is crucial, as chronic pain and disability can impact mental health and quality of life.