Spinal cord stimulation attenuates temporal summation in patients with neuropathic pain

Evidence has shown that electrical stimutatjon at the ciorsal columns attenuated the wind-up phenomenon in dorsal horn neurons in nerve-injured rats. This study was aimed to test the effect of spinal cord stimulation (SOS) on temporal summation (TS), the clinical correlate of the wind-up phenomenon in patients with radicular leg pain. Eighteen patients with SOS implants were tested both 30 minutes after SOS activation (ON) and 2 hours 'after turning it off (OFF), in a random order. Temporal summation was evaluated in the most painful site in the affected leg and in the corresponding area in the contralateral leg by applying a tonic painful heat stimulus (46.5 degrees C; 120 seconds) and simultaneous recording of the perCeived heat pain intensity. Patients were also requested to report their clinical pain intensity (0-100 numerical pain scale) during SOS ON and OFF. The Wilcoxon signed rank test was used in the comparisons between SOS ON and OFF. Spinal cord stimulation activation significantly attenuated clinical pain intensity (from 66 +/- 18 to 27 +/- 31, P < 0.001). In the nonpainful leg, SOS activation failed to produce an effect on TS (24 +/- 20 vs 21 +/- 24 in SOS OFF and ON, respectively; P = 0.277). In contrast, a significant decrease in the magnitude of TS in the affected leg was observed in response to SOS activation (from 32 +/- 33 to 19 +/- 24; P = 0.017). These results suggest that attenuation of, TS, which likely represents suppression of hyperexcitability in spinal cord neurons, is a possible mechanism underlying SOS analgesia in patients with neuropathic pain.