Somatosensory evoked potential changes following electro-acupuncture therapy in chronic pain patients

Somatosensory evoked potentials were recorded in 20 healthy volunteers and 20 patients with chronic pain undergoing electro-acupuncture therapy. The values of absolute peak latency and amplitudes of N19 and P22 in the control group were compared with the corresponding baseline values in the study group and after electro-acupuncture therapy at three stages during a 10-treatment cycle. On these occasions the intensity of pain was recorded using a 100 mm visual analogue scale score. Each patient in the study group had 10 treatments given on alternate days. The absolute peak latency of N19 was significantly delayed (p < 0.05) in chronic pain patients when compared to the control group. This increase in latency of N19 persisted after the first electro-acupuncture treatment (p < 0.05), tended to revert to normal after the fifth treatment (p > 0.05) and reverted completely to control values after the 10th treatment (p > 0.05). Visual analogue scores also decreased significantly (p < 0.05) after the fifth and 10th electro-acupuncture sessions. These observations suggest that there is an interaction of the neural mechanisms of electro-acupuncture with the thalamic generator of somatosensory evoked potentials i.e. N19.