LAS VEGAS—Understanding factors that influence the outcomes of TENS (transcutaneous electrical nerve stimulation) can improve its clinical efficacy, Kathleen A. Sluka, PT, PhD, professor of physical therapy and rehabilitation science at the University of Iowa Carver College of Medicine, Iowa City, Iowa, said in a review of the modality for pain management.
TENS, the application of electrical stimulation to the skin for pain control, works by activating large diameter afferent fibers, reducing central excitability and activating descending inhibitory pathways. The treatment is noninvasive, inexpensive, and can be applied by the patient.
Dr. Sluka presented evidence in support of TENS. A rigorous metaanalysis with data from 29 randomized trials that included patients with pain from the back, hip, neck, and knee found TENS had a favorable pooled effect when compared with placebo (P<.0005). In two other studies, TENS was also shown to be clinically effective in patients with osteoarthritis and, in those with postoperative pain from abdominal surgery, TENS reduced pain with movement (ie, walking and deep breathing) and improved gait speed and distance; however, there was no change in pain at rest. High frequency TENS was found to be effective for dysmenorrhea and acupuncture- like TENS (but not continuous TENS) beneficial for rheumatoid arthritis of the hand.
Factors that affect TENS efficacy include selecting appropriate patient populations, an understanding of mechanisms (drug interactions, tolerance with repeated use), dosing (intensity and frequency), and outcome measurements (pain at rest and with movement, timing of outcome measurement, and function, quality of life, and pain physiology). Factors related to outcome assessment include time; ie, whether the patient is assessed during or immediately after TENS as well as the outcome measured: resting pain, movement pain, hyperalgesia, function, or quality of life. Multiple outcome measures that incorporate diverse measures can more completely assess effectiveness of treatment.
Dr. Sluka made the following recommendations for optimization of TENS application. First, the electrodes should be placed at the site of pain and applied during physical activity or exercise. Second, the frequency should be modulated between low and high, with the intensity as high as the patient can tolerate, with duration a minimum of 20 to 30 minutes. Third, patients should be made aware of the potential for drug interactions and be advised to use high frequency when taking concomitant opioids. Finally, the clinical population should be carefully selected.