Paired associative stimulation after spinal cord injury: who should undergo?

Abstract

Background: Paired associative stimulation (PAS) combines peripheral nerves stimulation (PNS) with transcranial magnetic stimulation (TMS) and it is believed to induce plastic changes in the human corticospinal tract after spinal cord injury (SCI). The aim of the present study was to investigate the advantages of PAS added to conventional rehabilitation protocol for patients with chronic SCI. Methodology: The study was monocentric sham-controlled and involved 11 patients with lower paraparesis 3-12 months after the trauma. TMS was delivered over vertex using a round coil with 150% of resting threshold. ESPN of both n. peroneous and n. tibialis was performed with supramaximal intensity at fossa poplitea for 5 minutes for each nerve. The interval between TMS and PNS was individually defined (around 35ms). The intervention consisted 30 sessions of 1Hz PAS in total. Results: After the intervention, the improvement of motor and sensory function (via ASIA impairment scale) was observed in both groups but the intergroup difference was insignificant (Mann–Whitney U test, p=0.0675). Spasticity (via modified Ashworth scale) was not changed significantly but 4 patients noticed more uncontrolled movements. Expectedly, patients with no peripheral M-response at the beginning do not demonstrated any improvements. The best functional outcome was found into patients with preserved MEP in the study group. Two patients with absent MEP at the beginning from the study group showed unstable MEP after a month. Conclusion: PAS could be seen as an additional tool to facilitate the recovery after chronic SCI. Patients with preserved MEP may benefit more from this technique. On the other hand, the absence of M response could be considered as an exclusion criterion while the selection of individuals for PAS. The choice of stimulation protocols is still arguable that can lead to diverse and controversial results.