Usefulness of the coherence entrainment test for deep brain stimulation for a patient with atypical tremor.

A 40-year-old man with an anxiety disorder developed sudden-onset right-hand tremor after a fixation wire for a tibial bone fracture was removed. He manifested a resting and action tremor with an irregular pattern. A coherence entrainment test (CET) revealed that the peak power spectral frequency of the right finger tremor was not entrained by simultaneous voluntary left finger tapping, which indicated a non-psychogenic origin. Deep brain stimulation to the left thalamic ventral intermediate nucleus abolished the tremor. We concluded that CET can determine the surgical indications for an unusual tremor that must be differentiated from that of psychogenic origin.