DOES THE STIMULUS FREQUENCY AFFECT THE ANALGESIC RESPONSE TO ELECTRICAL STIMULATION? (1999)

S210 INTRODUCTION: Use of non-pharmacologic neuromodulation therapies like percutaneous electrical nerve stimulation (PENS) have been reported to be effective in relieving both acute and chronic pain syndromes [1,2]. However, the effect of the frequency of the electrical stimulation has not been studied. Therefore, we designed a randomized, sham-controlled, cross-over study to compare the effects of sham-PENS with PENS at frequencies 4 Hz, alternating 15 Hz and 30 Hz (15/30 Hz), and 100 Hz on the analgesic response, physical activity and quality of sleep in patients with low back pain (LBP). METHODS: Sixty-eight consenting patients with LBP secondary to degenerative disc disease were treated with sham-PENS and three different frequencies of PENS therapies according to a randomized, cross-over IRB-approved study. For the PENS treatments, the electrical stimulus was applied to 10, 32 ga. acupuncture-like needles placed at the lumbar dermatomes corresponding to the patient's pain symptoms. However, no electrical stimulation from a low-output (5 mAmp) generator was applied to the needle probes for the sham-PENS treatments. Each PENS treatment was administered for a period of 30 min three times per week for 2 weeks at frequencies (F) of 0 (sham-PENS), 4, 15/30 or 100 Hz (in a random sequence). All patients had been maintained on a stable oral analgesic treatment regimen for at least 3 months prior to entering the study. The pre-treatment assessment included visual analog scales (VAS) for pain, physical activity and quality of sleep (with 0=best to 10=worst). After receiving all four modalities, patients completed a global assessment questionnaire comparing the relative effectiveness of the different stimulation frequencies. RESULTS: All three frequencies of PENS therapy were effective in acutely decreasing pain, as well as in improving the physical activity and quality of sleep (* vs sham-PENS, p-value < 0.05). However, these data indicate that the alternating 15/30 Hz treatments produced a greater benefit over the course of the 2-week treatment period ([dagger] vs F 4 and F 100, p-value < 0.05). The daily oral analgesic requirements were also significantly decreased over the course of the 2-week treatment period with the all three PENS frequencies, but not with the sham-PENS therapy. The overall percentage decrease in the oral non-opioid analgesic requirements was again significantly greater with alternating 15/30 Hz than with 4 Hz, 100 Hz or sham treatments (Table 1). In the overall assessment, 40% of the patients reported that F 15/30 was the most effective modality in relieving their pain. Compared to all other modalities, the F 15/30 treatments were also more effective in improving the patient's sense of "well-being" and their willingness to pay "out of pocket" to receive the therapy in the future.Table 1DISCUSSION: Given the interest of both patients and healthcare providers in complementary medical therapies [3], it is not surprising that non-pharmacologic analgesic therapies involving electrical stimulation (e.g., PENS,) are becoming increasingly popular. Of the three frequencies of electrical stimulation utilized in this cross-over study, the alternating 15/30 Hz frequency treatments appeared to be the optimal frequency for patients with LBP.