[The varied etiologies of childhood-onset dystonia]

Dystonia is not uncommon in childhood, and identification of its etiology is an ultimate aim in the clinical evaluation of dystonia. Advances in neuroimaging, recent identification of gene or loci implicated in dystonic syndromes, and characterisation of new pathological entities (creatine deficiency, biotin-responsive basal ganglia disease) enlarge our understanding of childhood dystonia, and expend its diagnosis spectrum. Awareness of the diverse etiologic categories of childhood-onset dystonia is necessary to accurate diagnosis approach. Clinical examination and cerebral magnetic resonance imaging are the keys of this diagnosis approach. Primary dystonia is defined as syndromes in which dystonia is the sole phenotypic manifestation (especially no cognitive deterioration is observed, and brain MRI is normal); DYT1 dystonia, in which the abnormal gene is located on chromosome 9, is the most frequent childhood-onset primary dystonia; progressive generalisation of the abnormal movements occur in 70p.cent of the patients. Dopa - Responsive Dystonia are characterized by marked diurnal fluctuations of the dystonic symptoms and by their marked and sustained response to dopaminergic therapy; associated parkinsonian signs are usually observed later in the course of the disease. Clinical presentation of DRD might be atypical (mimicking cerebral palsy or isolated limb pain without diurnal fluctuation). DRD is rare, but a trial of L-dopa should be performed on all patients with childhood-onset dystonia, lasting at least one month. Secondary dystonias or heredodegenerative diseases are the most frequent etiology of childhood-onset dystonic syndromes. Among a huge range of heredodegenerative disease, those that are amenable to a specific treatment, such as Wilson's disease or creatine deficiency, should be particularly investigated. The main objective of investigation of dystonia is to identify secondary dystonias or heredodegenerative diseases. Further investigations will be performed according to the clinical characteristics of the dystonia, to the presence of associated neurological or extraneurological symptoms, and according to brain imaging; this approach must be discussed for each single patient. The aim of the diagnosis strategy is the rapid identification of the etiology of dystonia which will lead to accurate treatment and pertinent genetic counselling.