LATERALITY OF ONSET IN IDIOPATHIC TORSION DYSTONIA

Idiopathic torsion dystonia (ITD) is a dominantly inherited disorder w ith incomplete penetrance. It is important to identify factors that ma y cause dystonia or prevent its occurrence in a genetically predispose d individual. Because dystonia may be precipitated by peripheral trigg ers, we have investigated whether the preferential use of a limb affec ts the development of dystonia. Analysis of the correlation between th e side of motor dominance and the limbs in which dystonic symptoms fir st appeared was performed in 49 patients with ITD ascertained in a cou ntry-wide survey in Israel. The dominant motor side was determined in 45 cases (92%). Among 29 patients with lateralized limb onset, 24 show ed right-side motor dominance, of whom 21 had dystonia onset in a righ t limb. The first sign was in a left limb for all five cases with left -side motor dominance (90% coincidence). The pattern of limb involveme nt was studied. Detection bias could be ruled out. The highly signific ant relationship between the motor dominance and the laterality of lim b onset in ITD patients suggests that the preferred use of a limb may trigger the onset of dystonia.