Resetting tremor by single and paired transcranial magnetic stimulation in Parkinson’s disease and essential tremor

• Single- and paired-pulse transcranial magnetic stimulation (TMS) provide a useful opportunity to test non-invasively tremor pathophysiology in Parkinson’s disease (PD) and essential tremor (ET).
• The tremor-resetting index (RI) differentiated the functional roles of primary motor cortex (M1) and supplementary motor area (SMA) in PD vs. ET tremor.
• M1-TMS resulted in a higher RI in PD than ET, suggesting a stronger M1 involvement in PD resting and postural tremor than ET postural tremor.

ObjectiveThe pathogenesis of tremor in Parkinson’s disease (PD) and essential tremor (ET) is not fully understood. This study tested the role of primary motor cortex (M1), supplementary motor area (SMA) and cerebellar cortex on PD and ET tremor by single- and paired-pulse transcranial magnetic stimulation (TMS).MethodsTen PD patients with resting tremor, six of them also with postural tremor, and ten ET patients with postural tremor were studied. Randomized single- and paired-pulse TMS with an interstimulus interval of 100 ms were delivered over M1, SMA and cerebellum. TMS effects were evaluated by calculating a tremor-resetting index (RI).ResultsSingle- vs. paired-pulse TMS showed no difference. M1-TMS and SMA-TMS but not by cerebellar TMS induced a significant RI in PD and ET. M1-TMS resulted in a significantly higher RI in PD than ET. Furthermore, M1-TMS in PD but not in ET resulted in a significantly higher RI than SMA-TMS.ConclusionsFindings suggest a stronger involvement of M1 in resting and postural tremor in PD than postural tremor in ET.SignificanceRI provides a useful marker to explore the differential functional role of M1, SMA and cerebellum in PD vs. ET tremor.