Dystonia in Children
Dystonia is a hyperkinetic movement disorder characterized by sustained or intermittent muscle contractions that cause abnormal, often repetitive, twisting movements or postures. The condition arises from dysfunction in the basal ganglia, which are critical for controlling voluntary movement. In children, dystonia can be a complex and challenging condition to diagnose due to its varied presentation and multiple underlying causes. It can be a standalone symptom or part of a more extensive neurological disorder.
Classification and Causes
Dystonia can be classified based on its distribution and cause.
Focal: Affects a single body part, e.g., torticollis (neck) or blepharospasm (eyelids).
Generalised: Affects multiple body parts and can be progressive.
The aetiology is broad and can be categorised as primary (genetic) or secondary (symptomatic).
Primary (Genetic) Dystonias
Dopa-Responsive Dystonia (DRD): This is a key diagnosis to consider. The most common type is DYT-GCH1, inherited in an autosomal dominant pattern. It typically presents in childhood with a progressive foot dystonia, often causing an abnormal gait that worsens throughout the day. The diagnosis is confirmed by a dramatic and sustained response to a trial of low-dose levodopa.
Other genetic forms: These include a wide range of inherited conditions, such as DYT-TH and DYT-SPH.
Secondary (Symptomatic) Dystonias
These are caused by an underlying condition that damages the basal ganglia.
Perinatal Injury: Hypoxic-ischaemic encephalopathy (HIE) is a common cause.
Neurodegenerative and Metabolic Disorders: Examples include Wilson’s disease, Batten’s disease, mitochondrial diseases, and Glutaric aciduria type 1.
Infections: Post-infectious or autoimmune conditions such as Anti-NMDA receptor encephalitis can cause severe dystonia.
Medication: Dystonia can be an adverse effect of certain drugs, particularly neuroleptics.
Clinical Presentation
The clinical presentation of dystonia is highly variable and can be subtle.
Abnormal Postures: The child may have sustained, involuntary postures, such as fisting of the hands, turning of the feet, or a twisting motion of the trunk.
Gait and Speech: Dystonia often first becomes noticeable when the child is performing a specific task, such as walking or speaking. The gait may be abnormal, and the child’s speech may be slurred.
Sleep: A key diagnostic feature is that dystonia typically resolves during sleep.
Pain: Dystonia, especially of the neck (torticollis), can be painful.
Investigations
Investigations are guided by the clinical presentation and are aimed at identifying a treatable cause.
Trial of Levodopa: In the absence of a clear cause, a trial of levodopa is often initiated to rule out dopa-responsive dystonia. A positive response is diagnostic.
MRI Brain: An MRI is crucial to rule out structural causes, such as brain tumours, or to identify characteristic findings of metabolic disorders.
Metabolic and Genetic Screens: These include urine organic acid and amino acid screens, blood tests (e.g., CK, lactate), and genetic panels for known dystonia genes.
Management
Management is primarily symptomatic and is best handled by a multidisciplinary team including a paediatric neurologist, physiotherapist, occupational therapist, and speech and language therapist.
Pharmacological Therapy:
Levodopa: The first-line treatment for suspected dopa-responsive dystonia. A low dose is initiated and slowly titrated.
Oral Medications: Other medications that can help include trihexyphenidyl, baclofen, clonazepam, and gabapentin.
Focal Dystonia: Botulinum toxin injections are very effective for focal dystonias, such as torticollis, by temporarily weakening the overactive muscles.
Surgical Options: In severe, refractory cases, deep brain stimulation (DBS) or intrathecal baclofen may be considered.
Supportive Care: This is vital for improving quality of life. Physical therapy is essential to prevent joint contractures and maintain mobility. Occupational therapy helps with activities of daily living, and speech and language therapy can address any speech difficulties.