Lasting effects of repeated rTMS application in focal hand dystonia

Abstract

Purpose: Focal hand dystonia (FHD) is a rare but potentially devastating disorder involving involuntary muscle spasms and abnormal posturing that impairs functional hand use. Increased cortical excitability and lack of inhibitory mechanisms have been associated with these symptoms. This study investigated the short- and long-term effects of repeated administrations of repetitive-transcranial magnetic stimulation (rTMS) on cortical excitability and handwriting performance.

Methods: Six subjects with FHD and nine healthy controls were studied. All subjects with FHD received rTMS (1Hz) to the premotor cortex (PMC) for five consecutive days; of those, three subjects received five days of sham rTMS completed ten days prior to real treatment. Healthy subjects received one real rTMS session. Cortical silent period (CSP) and measures of handwriting performance were compared before and after treatment and at ten-day post-treatment follow-up.

Results: At baseline, significant differences in CSP and pen pressure were observed between subjects with FHD and healthy controls. Differences in CSP and pen velocity between subjects in real and sham rTMS groups were observed across treatment sessions and maintained at follow-up.

Conclusions: After five days of rTMS to PMC, reduced cortical excitability and improved handwriting performance were observed and maintained at least ten days following treatment in subjects with FHD. These preliminary results support further investigation of the therapeutic potential of rTMS in FHD.

Fig. 1

rTMS set-up used for cortical excitability assessment and treatment.

Fig. 2

Top: Force trace during CSP measurement. Box highlights the increased force production due to superimposed rTMS excitation and the resulting decreased force during CSP before voluntary force return. Bottom: Rectified EMG trace demonstrating CSP.

Fig. 3

Mean CSP, tracing error, pen pressure, pen velocity and fluency before rTMS application across groups (± SE). Significant differences between healthy and both patient groups in CSP and pen pressure are observed,^*p = 0.004, ^**p < 0.0005.

Fig. 4

A) CSP change across assessments between subjects receiving real versus sham rTMS (± SE). B) CSP change across treatment day (± SE). Significant silent period prolongation after five-day rTMS treatment application is observed and maintained at follow-up,^*p = 0.002, ^**p = 0.001.

Fig. 5

Change in pen velocity during loop tracing conditions across treatment day and follow-up assessment (± SE). Pen velocity increases across five-day rTMS treatment application are observed in the treatment group compared to the sham group, maintained at follow-up, ^*p = 0.05, ^**p = 0.007. Differences between groups at baseline with sham group subjects demonstrating higher velocities prior to rTMS, ^#p = 0.04.