WS2.3. TMS: Clinical Application of MEPs

Abstract

Transcranial magnetic stimulation (TMS) has utility for clinical assessment, studies of physiology, and therapy. There are a number of purposes in the clinic, particularly in regard to assessment of the corticospinal tract by central motor conduction velocity (CMCV). CMCV is obtained by getting the motor evoked potential (MEP) latency and subtracting the peripheral conduction time. Peripheral conduction time can be assessed with stimulation over the spine or with the F-wave technique. In situations such as multiple sclerosis and cervical myelopathy, central conduction time is prolonged. It can also be used to monitor corticospinal tract function during surgery. TMS can be useful in proving normal function in patients with functional paresis. Recently, it is also being investigated for evaluation of upper motor neuron function in patients with ALS. Excitability of the motor cortex in this circumstance is best assessed with threshold tracking. Another valuable use is for presurgical mapping to examine topography of functional cortex. This is most commonly done for motor function and language. Guidelines for optimal methodology for mapping have been published.