Clinical neurophysiological evaluation for simple motor tics

OBJECTIVE: To demonstrate the usefulness of neurophysiological evaluation to distinguish simple motor tics and functional myoclonus. METHODS: Careful clinical assessments, multichannel surface EMG, and EEG-EMG jerk-locked back-averaging were performed. RESULTS: Urge to move and ability to voluntarily suppress the movement were reported. EMG bursts showed variable duration and triphasic pattern of the antagonist muscles mimicking voluntary movements. Only the late component of the Bereitschaftspotential (BP2) was present prior to the involuntary movement onset. CONCLUSION: Combination of the isolated late BP, premonitory urge, and suppressibility leads to the diagnosis of simple motor tics rather than functional myoclonus. SIGNIFICANCE: The physiological approach in addition to careful clinical assessment is helpful to support the diagnosis of tic.