Paired associative stimulation for spinal cord injury rehabilitation : a case study

The purpose of this study was to replicate a paired associative stimulation (PAS) therapeutic intervention to improve the motor output in one tetraplegic individual’s hands. PAS is a paired brain and nerve stimulation method using transcranial magnetic stimulation (TMS) and peripheral nerve stimulation (PNS). Tetraplegia is a neurological injury to the spinal cord which hinders voluntary movement of upper and lower limbs, with varying degrees based on the level of the spinal cord which is severed. Utilizing a PAS protocol aims to target the neuroplasticity in the CST to improve motor function. The intervention was given for 6 weeks, with a total of 22 individual sessions. This intervention tested the clinical feasibility of a high PAS protocol, as it used slightly altered stimulation conditions compared to the original protocol. Physiotherapy assessments were conducted pre-, post-, and 1-month post-intervention. This was the main evaluation method to assess functional motor improvement in the hands. Average motor evoked potentials (MEPs) recordings were also measured using TMS at pre- and post-intervention. After 6 weeks of PAS therapy, functional motor output increased in both hands, which had been diminished due to the injury. In the left hand, all the stimulated muscles saw improvement in the functional measures (physiotherapy assessments). In the right hand, only two of the three stimulated muscles saw minor improvements (extensor digitorum and abductor pollicis brevis), due to the lack of visible MEPs, measured by the TMS, in the abductor pollicis brevis and the abductor digiti minimi. To conclude, the original PAS protocol was successfully modified to yield positive results. Further studies should be conducted in the future for a longer duration to validate the clinical feasibility.