P75-S Exploratory study of optimal stimulus parameters of repetitive transcranial magnetic stimulation for neuropathic pain

Abstract

Background The analgesic effect of 5-Hz repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex (M1) remained modest in patients with neuropathic pain (NP). The aim of the present study was to investigate analgesic effects of M1-rTMS at different stimulus parameters to explore an optimal stimulation condition for treating NP. Material and methods We conducted a randomized, blinded, crossover exploratory study. M1-rTMS at different parameters were administered in random order at least two weeks apart. The tested stimulus conditions were 5-Hz with 500 pulses per session; 10-Hz with 500 pulses; 10-Hz with 2,000 pulses; and sham stimulation. The outcome measures were a visual analogue scale (VAS), and the Short-form McGill Pain Questionnaire 2 (SF-MPQ-2). Statistical analyses were performed by a mixed-effect model (fixed effect: intervention, order, interaction between intervention and order; random effect: subject) and multiple comparisons. Results We enrolled 23 patients (11 men; mean age, 60.0 years) suffering from intractable neuropathic pain. There was a significant effect of intervention (i.e. stimulus condition) on VAS and SF-MPQ-2 (p = 0.03 and 0.01, respectively). Multiple comparisons with correction revealed that 10-Hz rTMS with 2,000 pulses provided better pain relief on VAS and SF-MPQ-2 compared to sham (p = 0.03 and 0.02, respectively). Conclusions The results of this study suggest that stimulus frequency and number of pulses should be taken into account for trials of M1-rTMS for treating NP.