Does the ability to stop ongoing movement differentiate cervical dystonia from functional cervical dystonia?

Functional Cervical Dystonia (FCD) is characterized by hyperkinetic movements resembling Cervical Dystonia (CD). Previous studies report impaired reactive inhibition in CD, reflected by prolonged optimum combination Stop Signal Reaction Time (ocSSRT). This study compared ocSSRT in FCD, CD, and healthy controls.

20 CD and 14 FCD patients were recruited along with 23 age-matched healthy controls. All participants used a battery-operated portable device that measured both median reaction time and ocSSRT. Subjects released a button following a GO (green) signal and attempted to abort the movement when a STOP (red) signal followed the GO cue after a short delay.

CD patients had significantly prolonged ocSSRT compared to FCD and healthy controls (CD: 373 ± 76 ms, FCD: 285 ± 80 ms, healthy: 248 ± 64 ms; CD vs FCD, p = 0.026; CD vs healthy, p < 0.001). No significant difference was found between FCD and healthy controls (p = 0.396). Median reaction time was significantly longer in CD (563 ± 117 ms) than healthy controls (466 ± 82 ms; p = 0.015), but not FCD (500 ± 117 ms; p = 0.296). The ROC curve AUC for ocSSRT distinguishing CD from FCD was 0.775 (p = 0.002).

ocSSRT may serve as a useful marker to differentiate CD from FCD in clinical settings.