Continuous theta-burst stimulation of the primary motor cortex in essential tremor

We investigated whether essential tremor (ET) can be altered by suppressing the corticospinal excitability in the primary motor cortex (M1) with transcranial magnetic stimulation.

10 Patients with ET and 10 healthy controls underwent transcranial continuous theta-burst stimulation (cTBS) of the left primary motor hand area at 80% (real cTBS) and 30% (control cTBS) of active motor threshold in two separate sessions at least one week apart. Postural tremor was rated clinically and measured accelerometrically before and after cTBS. Corticospinal excitability was assessed by recording the motor evoked potentials (MEP) from the first dorsal interosseous muscle.

Real cTBS but not control cTBS reduced the tremor total power assessed with accelerometry. This beneficial effect was subclinical as there were no significant changes in clinical tremor rating after real cTBS. Relative to control cTBS, real cTBS reduced corticospinal excitability in the stimulated primary motor cortex only in healthy controls but not in ET patients.

Real cTBS has a beneficial effect on ET. Since cTBS did not induce a parallel reduction in corticospinal excitability, this effect was not mediated by a suppression of the corticospinal motor output.

"Inhibitory" cTBS of M1 leads to a consistent but subclinical reduction in tremor amplitude.