Definitions: Dystonia is a muscle contraction disorder marked by sustained involuntary clonic contortions or abnormal posture. Primary dystonias can be divided into familial forms related to genetic anomalies and idiopathic forms. Secondary dystonias are related to an underlying neurological disease.
Metabolic diseases: Secondary dystonias related to metabolic diseases generally occur early before puberty although late onset forms have been described. Other signs, in association with the dystonia, include mental retardation, epilepsy, cerebellous or pyramidal signs, oculomotor disorders, or a neuropathy. Occasionally, extraneurological signs suggest the diagnosis. Biological markers are known for most of these dystonias. EVENT-RELATED DISEASES: In some cases, the dystonia is the only sign and develops as a sequela to an earlier neurological event such as neonatal anoxia, trauma, vascular event or adverse effect of neuroleptics. HEMI-DYSTONIAS: Dystonias limited to one side are generally secondary.