IS TENS PURELY A PLACEBO-EFFECT - A CONTROLLED-STUDY ON CHRONIC LOW-BACK-PAIN

Although high-frequency low-intensity transcutaneous electric nerve st imulation (TENS) has been extensively used to relieve low back pain, e xperimental studies of its effectiveness have yielded contradictory fi ndings mainly due to methodological problems in pain evaluation and pl acebo control. In the present study, separate visual analog scales (VA S) were used to measure the sensory-discriminative and motivational-af fective components of low back pain. Forty-two subjects were randomly assigned to 1 of 3 groups: TENS, placebo-TENS, and no treatment (contr ol). In order to measure the short-term effect of TENS, VAS pain ratin gs were taken before and after each treatment session. Also, to measur e long-term effects, patients rated their pain at home every 2 h throu ghout a 3-day period before and 1 week, 3 months and 6 months after th e treatment sessions. In comparing the pain evaluations made immediate ly before and after each treatment session, TENS and placebo-TENS sign ificantly reduced both the intensity and unpleasantness of chronic low back pain. TENS was significantly more efficient than placebo-TENS in reducing pain intensity but not pain unpleasantness. TENS also produc ed a significant additive effect over repetitive treatment sessions fo r pain intensity and relative pain unpleasantness. This additive effec t was not found for placebo-TENS. When evaluated at home, pain intensi ty was significantly reduced more by TENS than placebo-TENS 1 week aft er the end of treatment, but not 3 months and 6 months later. At home evaluation of pain unpleasantness in the TENS group was never differen t from the placebo-TENS group. These results suggest that TENS reduces both the sensory-discriminative and motivational-affective components of low back pain in the short term but that much of the reduction in the affective component may be a placebo effect. We conclude that TENS should be used as a short-term analgesic procedure in a multidiscipli nary program for low back pain rather than as an exclusive or long-ter m treatment.