Using EMG to Determine TMS Motor Thresholds

Link to study: Badran et al. 2019

Overview

Resting motor threshold (rMT) determination is important for safe and effective transcranial magnetic stimulation (TMS). rMT determination methods include visual observation (VO) or electromyography (EMG). Many TMS providers do not have access to EMG equipment, so VO was explored as an alternative in early TMS development. Pridmore and colleagues (1998) demonstrated that rMT determined by observation of TMS-induced visible movement caudal to the wrist was roughly equivalent to EMG [1]. Neuronetics used VO for their pivotal trial [2], however other trials used EMG [[3], [4], [5]]. Additionally, Parameter Estimation by Sequential Testing (PEST) further improved VO rMT determination [6,7].

The Pridmore study contained only 6 subjects and no one has since formally compared VO to EMG rMT. One study demonstrated that given a single muscle, EMG produces lower rMT than does visual movement of that isolated muscle [8]. VO of the muscles caudal to the wrist, the clinically adopted method, was not examined. We reexamined this important question.