Laterality of onset in idiopathic torsion dystonia.

Idiopathic torsion dystonia (ITD) is a dominantly inherited disorder with incomplete penetrance. It is important to identify factors that may cause dystonia or prevent its occurrence in a genetically predisposed individual. Because dystonia may be precipitated by peripheral triggers, we have investigated whether the preferential use of a limb affects the development of dystonia. Analysis of the correlation between the side of motor dominance and the limbs in which dystonic symptoms first appeared was performed in 49 patients with ITD ascertained in a country-wide survey in Israel. The dominant motor side was determined in 45 cases (92%). Among 29 patients with lateralized limb onset, 24 showed right-side motor dominance, of whom 21 had dystonia onset in a right limb. The first sign was in a left limb for all five cases with left-side motor dominance (90% coincidence). The pattern of limb involvement was studied. Detection bias could be ruled out. The highly significant relationship between the motor dominance and the laterality of limb onset in ITD patients suggests that the preferred use of a limb may trigger the onset of dystonia.