Indication of central sensitization in chronic neuropathic pain after spinal cord injury.

BACKGROUND Central sensitization is considered a key mechanism underlying neuropathic pain (NP) after spinal cord injury (SCI). METHODS Two novel proxies for central sensitization were investigated in thoracic SCI subjects with (SCI-NP) and without NP (SCI-nonNP) compared to healthy controls (HC). Specifically, temporal summation of pain (TSP) was investigated by examining pain ratings during a 2-min tonic heat application to the volar forearm. Additionally, palmar heat-induced sympathetic skin responses (SSR) were recorded in order to reveal changes in pain-autonomic interaction above the lesion level. Pain extent was assessed as the percentage of body area and the number of body regions being affected by NP. RESULTS Enhanced TSP was observed in SCI-NP (+66%) compared to SCI-nonNP (-75%, p=0.009) and HC (-59%, p=0.021). In contrast, no group differences were found (p=0.685) for SSR habituation. However, pain extent in SCI-NP was positively correlated with deficient SSR habituation (body area: r=0.561, p=0.024; body regions: r=0.564, p=0.023). CONCLUSIONS These results support the value of TSP and heat-induced SSRs as proxies for central sensitization in widespread neuropathic pain syndromes after SCI. Measures of pain-autonomic interaction emerged as a promising tool for the objective investigation of sensitized neuronal states in chronic pain conditions