I-wave periodicity transcranial magnetic stimulation (iTMS) on corticospinal excitability. A systematic review of the literature

Repetitive transcranial magnetic stimulation (rTMS) is an established technique that can modulate excitability of the motor cortex and corticospinal tract, beyond the duration of the stimulation itself. More recently, a newer repetitive technique, known as I-wave periodicity TMS (iTMS) has been purported to show increases in corticospinal excitability following at least 10 min of iTMS duration. The aim of this study was to use a systematic review to search the literature from January 2000 to October 2015 with regard to corticospinal outcomes following iTMS intervention. We also rated the quality of studies and assessed the risk of bias by applying the Downs and Black checklist and the Cochrane Collaboration Risk of Bias Tool respectively. From an initial yield of 144, 11 studies were included. Studies were found to be of moderate quality, however a high risk of bias was identified. Despite these issues, evidence from the studies presented in this review so far indicates that iTMS is effective in increasing corticospinal excitability. However, further studies are required from other groups to validate the findings to date. Additional research is required to reduce the variability in corticospinal excitability and also to functional outcomes along with corticospinal excitability following iTMS.