Abnormal movement disorders are classified as parkinsonism, dystonia, tremor, chorea, myoclonus, tics, stereotypies, and complex movement disorder. Dystonia is described as contraction of both agonist and antagonist muscles simultaneously, causing twisting and repetitive movements or abnormal postures. The earlier the age of onset, the more generalised and severe the condition tends to be.
Dystonic movements are patterned and sustained. They repeatedly involve the same muscle groups. The urge to perform the dystonic movements is absent, and there is no relief after the dystonic movements are executed. Dystonia usually gets worse with fatigue and emotional stress and it gets better with sleep and relaxation. Photographs and video footage of affected infants are helpful in delineating the dystonic movements. Periodic follow-up is often a prerequisite to making an accurate diagnosis.
Types of infantile dystonia
Clinical characteristics (axis 1), which include age at onset, body distribution, temporal pattern, and associated features
Atiology (axis 2), which includes nervous system pathology and inheritance.
Information from the history and physical examination allows an initial classification and differential diagnosis to be made. The presence and absence of motor features and other signs and symptoms can narrow the differential diagnosis by indicating a particular dystonia syndrome and by directing the diagnostic evaluation towards groups of disorders associated with different clinical patterns, such as:
Isolated dystonia (dystonia alone or dystonia with tremor)
Combined dystonia (dystonia with other motor features)
Complex dystonia (dystonia with other symptoms).
The clinical evaluation may also indicate whether the condition is neurodegenerative or suggest an acquired or inherited aetiology.
Further investigations may be required including neuroimaging, evaluation for associated neurodevelopmental or systemic abnormalities, therapeutic trial of levodopa, or biochemical (including diagnostic lumbar puncture) and genetic tests.
Several pseudo-dystonias need to be considered in the differential diagnosis; these conditions involve dystonia-mimicking abnormal movements, but their aetiologies differ from those of dystonias.
The rapid identification of several conditions is important to prevent irreversible injury or death:
Drug-induced acquired dystonia
Pseudo-dystonia due to cervical instability
Multiple neurometabolic disorders, such as glutaric aciduria type I
Acute bilirubin encephalopathy.
Dopa-responsive dystonia (Segawa syndrome, dystonia-parkinsonism with diurnal fluctuation) needs to be considered in any infant or child with unknown diagnosis and normal MRI. It is usually misdiagnosed as spastic diplegic or quadriplegic cerebral palsy, intractable epilepsy, or hereditary spastic paraplegia.
- Transient idiopathic dystonia of infancy
- Benign paroxysmal torticollis of infancy
- Congenital torticollis
- Primary paroxysmal kinesigenic dyskinesia (PKD)
- Drug-related dystonia
- Dyskinetic cerebral palsy
- Post-traumatic dystonia
- Non-fatal drowning
- Primary stereotypies
- Secondary stereotypies
- Secondary infantile torticollis (SIT)
- Primary paroxysmal non-kinesigenic dyskinesia (PNKD)
- Alternating hemiplegia of childhood (AHC)
- DYT-TOR1A (primary torsion dystonia)
- Dopa-responsive dystonia (Segawa syndrome, dystonia-parkinsonism with diurnal fluctuation)
- Paroxysmal exercise-induced dyskinesia glucose transporter 1 (GLUT1)
- Dopamine transporter deficiency syndrome (DYT/PARK-SLC6A3, infantile parkinsonism-dystonia)
- DYT-SGCE (myoclonus-dystonia syndrome)
- ADCY5-related dyskinesia (CHOR-DYT/ADCY5)
- Glutaric aciduria type I (glutaryl-CoA dehydrogenase [GCDH] deficiency)
- Methylmalonic acidaemia
- Lesch-Nyhan syndrome
- Infantile GM2 gangliosidosis (Tay-Sachs and Sandhoff's disease)
- Mitochondrial encephalomyopathies
- Allan-Herndon-Dudley syndrome (X-linked monocarboxylate transporter 8 deficiency)
- Biotin-thiamine-responsive basal ganglia disease (DYT-SLC19A3)
- Dopamine-serotonin vesicular transport disease
- Acquired paroxysmal kinesigenic dyskinesia (PKD)
- Acquired paroxysmal non-kinesigenic dyskinesia (PNKD)
- Neurodegeneration with brain iron accumulation (NBIA), including pantothenate kinase-associated neurodegeneration (PKAN)
- ARX-related disorders including infantile epileptic-dyskinetic encephalopathy
- Leukodystrophies/hypomyelinating disorders
- Aicardi-Goutieres syndrome (AGS)
- Other inherited neurodegenerative disorders with dystonia
- Paroxysmal tonic upgaze of infancy
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