The effect of pain quality on the efficacy of conventional TENS

The present study addressed the question of whether the quality of the pain experienced has an influence on the efficacy of transcutaneous electrical nerve stimulation (TENS). Forty pain free subjects were randomly assigned to experimental or control groups. Pre-test pain threshold and tolerance measures were obtained with two different instruments: a pressure dolorimeter and a forceps algometer. Subjects described the sensory quality of the induced pain using the sensory adjectives of the McGill Pain Questionnaire (MPQ). The experimental group was stimulated with conventional TENS for 20 minutes, and the control group with sham TENS for the same time period. Post-test pain threshold and tolerance were then measured. Subjects described the dolorimeter evoked pain as dull pressure and the forceps pain as sharp pinching. TENS significantly increased the pain threshold to the dolorimeter (p.05), but had no effect on the pain from the forceps. The shem TENS group exhibited a significant decrease in pain threshold to the dolorimeter (p.05), but no change in pain threshold to the forceps. No significant effects were found at pain tolerance levels. In summary, pain quality was found to influence the analgesic effect of TENS at the pain threshold level.