Eligible patients ( ie , those aged 18-75 years , disease duration 3 years , Toronto Western Spasmodic Torticollis Rating Scale [ TWSTRS ] severity score 15 points ) were randomly assigned ( 1:1 ) to receive active neurostimulation ( frequency 180 Hz ; pulse width 120 s ; amplitude 05 V below adverse event threshold ) or sham stimulation ( amplitude 0 V ) by computer-generated randomisation lists with randomly permuted block lengths stratified by centre .