Transcranial magnetic stimulation (TMS) is a non-invasive and painless method of stimulating neural activity within the corticospinal system (Tazoe and Perez, 2015). A coil is placed on the scalp over an area of interest (e.g. motor cortex) to generate an electromagnetic field, which alters electrical fields within the brain (Peterchev et al., 2012; Tazoe and Perez, 2015). Accordingly, this causes a change in neural membrane polarization, leading to an increase in neuron activity, transmission and activation of neural networks (Peterchev et al., 2012). This activity can be easily assessed using electromyographic recording electrodes to detect motor-evoked potentials (MEPs) – the output of the primary motor cortex (Tazoe and Perez, 2015). TMS may be applied as a single pulse or repetitively (rTMS) to elicit long-lasting significant improvements in aspects of sensory and motor function (Tazoe and Perez, 2015). The three main applications of rTMS in SCI are focused on improving sensory and motor function impairments, spasticity and neuropathic pain (Tazoe and Perez, 2015).
The methodological details and results from five TMS studies are listed in Table 16.
A limited number of studies have investigated the use of TMS in patients with SCI. The overall magnitude of improvements in functional outcomes was mixed. Significant improvements in muscle strength and functional task testing were observed in the majority of studies. Although, one study reported no significant change from baseline, while others reported mixed results based on the functional test used (e.g. pinch versus grasp). This might be related to the broad range of different methodologies used (e.g. stimulation parameters and types of patients). Regardless of these findings, TMS may be a promising approach to facilitate aspects of recovery after SCI. For example, Peterson and colleagues investigated the application of TMS after elbow extension reconstructive surgery and found enhanced motor recovery/plasticity. In conclusion, further research in this area is necessary to investigate potential applications of TMS and their functional contribution to SCI rehabilitation. Future research should focus on evaluating ADL and FIM outcomes, as well as rTMS in combination with other therapies.
There is level 1b evidence (from one randomized controlled trial; Tolmacheva et al., 2017) that TMS combined with PNS significantly improves muscle function of the hand.
There is level 1b evidence (from one randomized control trial; Gomes-Osman & Field-Fote, 2014) that rTMS may reduce corticospinal inhibition and enhance clinical/functional outcomes for several weeks after treatment.
There is level 2 evidence (from two prospective controlled trialz; Bunday et al., 2018; Bunday et al., 2014) that PCMS applied during voluntary activity may enhance spinal plasticity after SCI.
There is level 2 evidence (from one prospective controlled trial; Peterson et al., 2017) that TMS delivered to the motor cortex after elbow extension reconstructive surgery significantly improves elbow extension.
There is level 4 evidence (from one pre-post study; Belci et al., 2004) that TMS may lower intracortical inhibition and improve clinical motor scores.
rTMS has many applications and may improve functional outcomes alone or in combination with PNS and reconstructive surgery.