The effect of stimulus frequency on the analgesic response to percutaneouselectrical nerve stimulation in patients with chronic low back pain

Low back pain (LBP) is one of the most common medical problems in our socie ty. Increasingly, patients are turning to nonpharmacologic analgesic therap ies such as percutaneous electrical nerve stimulation (PENS). We designed t his sham-controlled study to compare the effect of three different frequenc ies of electrical stimulation on the analgesic response to PENS therapy. Si xty-eight consenting patients with LBP secondary to degenerative lumbar dis c disease were treated with PENS therapy at 4 Hz, alternating 15 Hz and 30 Hz (15/30 Hz), and 100 Hz, as well as sham-PENS (0 Hz), according to a rand omized, cross-over study design. Each treatment was administered for a peri od of 30 min three times per week for 2 wk. The pre- and posttreatment asse ssments included the health status survey short form and visual analog scal es for pain, physical activity, and quality of sleep. After receiving all f our treatments, patients completed a global assessment questionnaire. The s ham-PENS treatments failed to produce changes in the degree of pain, physic al activity, sleep quality, or daily intake of oral analgesic medications. In contrast, 4-Hz, 15/30-Hz, and 100-Hz stimulation all produced significan t decreases in the severity of pain, increases in physical activity, improv ements in the quality of sleep, and decreases in oral analgesic requirement s (P < 0.01). Of the three frequencies, 15/30 Hz was the most effective in decreasing pain, increasing physical activity, and improving the quality of sleep (P < 0.05). In the global assessment, 40% of the patients reported t hat 15/30 Hz was the most desirable therapy, and it was also more effective in improving the patient's sense of wellbeing. We conclude that the freque ncy of electrical stimulation is an important determinant of the analgesic response to PENS therapy. Alternating stimulation at 15-Hz and 30-Hz freque ncies was more effective than either 4 Hz or 100 Hz in improving outcome me asures in patients with LBP. Implications: The frequency of electrical stim ulation seems to be an important determinant of the analgesic efficacy of p ercutaneous electrical nerve stimulation. Mixed low- and high-frequency sti mulation was more effective than either low or high frequencies alone in th e treatment of patients with low back pain.