Somatosensory change and pain relief induced by repetitive transcranial magnetic stimulation in patients with central poststroke pain.

OBJECTIVE: To quantify changes in pain and somatosensory function in patients with central poststroke pain (CPSP) syndrome following five sessions of repetitive transcranial magnetic stimulation (rTMS).

METHODS: Fourteen CPSP patients underwent MRI-guided TMS mapping to identify the motor hotspot for evoked responses from a muscle corresponding to a painful region (hand, N = 11, or distal leg, N = 3). Targeted rTMS consisting of 2000 stimuli/10 Hz each session was delivered over five sessions. Quantitative somatosensory testing (QST) was performed within the painful area and at the contralateral mirror-image site at baseline and after the rTMS.

RESULTS: At baseline there were significant sensory deficits of the affected body side for warm and cold detection and heat/cold pain thresholds. Following rTMS, sensory thresholds showed significant improvements for cold detection threshold (repeated-measures ANOVA, p = 0.04). Subjects' pain reports (numerical rating scale 0-10) showed modest but significant improvements in the first week after rTMS (baseline 7.0 ± 1.5; post-TMS 6.3 ± 1.5; Wilcoxon signed-rank test, p = 0.018), and these were largely maintained for up to four weeks post-rTMS. Improvements in warm detection threshold showed a significant correlation with decrease in pain score (Spearman's rank-order correlation, p = 0.007).

CONCLUSIONS: Five sessions of open-label rTMS provided analgesia and improved thermal sensibility. The correlation of reduction of detection threshold for warmth and pain relief suggest that the effect of rTMS may be mediated via circuitries that share the processing of noxious and thermal signals, such as the insula and the somatosensory and anterior cingulate cortices. QST may have a role in the assessment of patients with neuropathic pain for suitability for rTMS treatment and is likely to add to our understanding of how rTMS induces pain relief.