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.