Functional motor symptom | Clinical features | Laboratory tests |
Tremor | Entrainment (tremor takes on the rhythm of paced movements performed with another body part) Pause with quick movement of another limb Variability in frequency, amplitude Tonic contraction at onset Increase in amplitude with weighting Coherence of tremor between two limbs Whack-a-mole sign (restraint of tremor induces tremor in another body part) | Clinical neurophysiological measurements can quantify entrainment, pause with quick movement, variability, tonic contraction at onset, increase amplitude with weighting and coherence between limbs |
Myoclonus | Variability and long duration of the movement Complex movement Appearance of startle Long and variable latency of stimulus induced jerks Jerks when tendon hammer stops short of contact | Long electromyography bursts Presence of a Bereitschaftspotential (readiness potential) before the jerk With stimulus-induced jerks: long and variable latency |
Tic | Lack of urge Lack of voluntary control (suppressibility) | Normal Bereitschaftspotential |
Dystonia | Certain patterns such as fixed dystonia or pulling lip to one side | Normal blink reflex recovery Normal plasticity with paired associative conditioning |
Parkinsonism | Marked slowness or incoordination in examination but not with normal movements Gegenhalten (variable resistance during passive movement) Lack of sequence effect (slowness without amplitude decrement during repetitive movements) Huffing and puffing sign (fatigue with minimal effort) | Normal dopamine transporter scan |
Gait disorders | Specific patterns including knee buckling, dragging a monoplegic leg, astasia-abasia, excessive slowness and atypical limping Better balance than claimed, including improvement with distraction Either no falls, controlled falls or falling toward support Chair test (can use legs to move a chair better than walking) | None |