COMPARATIVE EFFECTIVENESS OF DIFFERENT STIMULATION MODES IN RELIEVING PAIN .3. A DOUBLE-BLIND CONTROLLED LONG-TERM CLINICAL-TRIAL

Part I of our earlier pilot study demonstrated that patients preferred modulated stimulation forms - frequency modulation and burst - rather than conventional continuous mode. To assess whether long-term therapeutic effects validate the immediate test results, this trial was performed in 14 patients with 21 pain conditions. Considering the results of the pilot study, the test stimulator was modified and 4 different forms of transcutaneous electrical nerve stimulation were randomly delivered to each patient who was blind to the modes of stimulation for 20 min. A second observer assessed the pain scores using visual analogue scales. The stimulation modes employed were: (1) conventional continuous stimulation (continuous pulses with a constant frequency of 70 Hz), (2) burst stimulation (80 msec long trains of pulses, each train consisting of 8 pulses, with an internal frequency of 90 Hz repeated 1.3 times a second), (3) high-rate frequency modulation, HRFM (continuous pulses changed from 90 Hz to 55 Hz over 90 msec, 1.3 times a second), (4) low-rate frequency modulation, LRFM (continuous pulses changed from 60 Hz to 20 Hz over 90 msec, 1.3 times a second). After the test treatment of 4 sessions in the clinic, depending on the pain scores and duration of pain relief recorded, the most effective stimulation mode was determined for each patient and a portable stimulator preset appropriately for that mode was given to be used at home, under our supervision, for 3 months. Fourteen pain conditions out of 21 (66%) responded well to the therapy; the majority preferred was the HRFM and burst-type stimulation. These results validate the initial testing of different stimulation modes before assessing long-term stimulation therapy.