Modulatory effect of continuous theta burst stimulation in patients with essential tremor

Introduction: We aimed to study the cortical and intracortical functions in patients of ET using transcranial magnetic stimulation (TMS) and to evaluate the effect of continuous theta burst stimulation (cTBS) on the tremor characteristics. Methods: Ten ET and 20 healthy controls were included in the study. All the participants were evaluated with TMS with recording of resting motor threshold (RMT), central motor conduction time, contralateral silent period (cSP), short interval intracortical inhibition (SICI) and intracortical facilitation (ICF). Subsequently only ET patients underwent cTBS of the motor cortex (Ml) followed by repeat TMS. Results: The mean age of the patients (46.5 + 17.2 years) was comparable to healthy controls (55.4 + 9.2 years; p = 0.16). There was a non-significant increase in RMT in ET patients (44 + 12.5%) when compared to healthy controls (40.9 + 6.9%; p = 0.48). There was a significant reduction of cSP in the ET group (102.03 + 15.26 msec) compared to healthy controls (116.1 + 15.2, p = 0.03). In addition, a significant reduction in ICF was observed in ET patients (0.9 + 0.7) compared to healthy controls (1.8 + 0.8, p = 0.01). Following cTBS there was a significant reduction in the tremor scores [FTMRS (Pre-cTBS: 29.3 + 18.7, Post-cTBS: 25.3 + 16.8; p < 0.001) and TETRAS (pre-cTBS: 34.4 + 16.2, post-cTBS: 29.8 + 12.1; p = 0.01)] and improvement (increase) of the duration of cSP (pre-cTBS: 102.03 + 15.3 msec., post-cTBS: 119.4 + 12.03 msec; p = 0.05). Conclusions: Patients with ET have GABAergic and glutaminergic dysfunction as demonstrated by reduced cSP and ICF. However, only the cSP improved following cTBS of Ml region, with a corresponding improvement of tremor severity suggesting the effect of cTBS on the cerebello-thalamo-cortical network.