Patient-delivered tDCS on chronic neuropathic pain in prior responders to TMS (a randomized controlled pilot study)

Background: Successful response to repetitive transcranial magnetic stimulation (rTMS) of the motor cortex requires continued maintenance treatments. Transcranial Direct Current Stimulation (tDCS) may provide a more convenient alternative. Methods: This pilot study aimed to examine the feasibility of a randomized, double-blind, double-crossover pilot study for patients to self-administer tDCS motor cortex stimulation for 20 minutes/day over five consecutive days. Primary outcomes were as follows: usability of patient-administered tDCS, compliance with device, recruitment, and retention rates. Secondary outcomes were as follows: effect on overall pain levels and quality of life via Short Form-36 anxiety and depression via Hospital Anxiety and Depression Scale, and Mini-Mental State scores. Results: A total of 24 subjects with neuropathic pain, who had previously experienced rTMS motor cortex stimulation (13 with reduction in pain scores, 11 nonresponders) were recruited at the Pain Research Institute, Fazakerley, UK. A total of 21 subjects completed the study. Recruitment rate was 100% but retention rate was only 87.5%. All patients reported satisfactory usability of the tDCS device. No significant difference was shown between Sham vs Anodal (-0.16, 95% CI: -0.43 to 0.11) P=0.43, Sham vs Cathodal (0.11, 95% CI: -0.16 to 0.37) P=0.94, or Cathodal vs Anodal (-0.27, 95% CI: -0.54 to 0.00) P=0.053 treatments. Furthermore, no significant changes were demonstrated in anxiety, depression, or quality of life measurements. The data collected to estimate sample size for a definitive study suggested that the study's sample size was already large enough to detect a change of 15% in pain levels at 90% power for the overall group of 21 patients. Conclusion: This study did not show a beneficial effect of tDCS in this group of patients and does not support the need for a larger definitive study using the same experimental paradigm. Trial registration: ISRCTN56839387.