Quantitative meta-analysis of grey matter anomalies in neuropathic pain.

Background: Increasing neuroimaging studies have revealed grey matter (GM) anomalies of several brain regions by voxel-based morphometry (VBM) studies in patients with neuropathic pain. The changes have been suggested to be related to central sensitization. Our aim was to investigate concurrence across VBM studies to identify whether different subtypes of neuropathic pain share a common pathophysiological basis revealed by structural abnormalities. Methods: A systematic search of VBM studies of patients with neuropathic pain and healthy controls published in PubMed and Embase databases from January 2000 to March 2014 was conducted. A quantitative meta-analysis of whole-brain VBM studies in patients with neuropathic pain compared with healthy controls was performed by means of effect-size signed differential mapping. Results: Ten studies comprising 240 patients with neuropathic pain and 263 healthy subjects were systematically included in the present study. Compared to healthy controls, the patients showed consistent decreased GM in bilateral anterior insula and thalamus, right superior frontal gyrus and left postcentral gyrus, and increased GM in right medial frontal gyrus and right posterior insula. The results remained largely unchanged in the following jackknife sensitivity analysis. Conclusions: This meta-analysis shows strong evidence of brain GM anomalies within the pain matrix in patients with neuropathic pain compared with healthy subjects. Further studies are needed to determine whether the reported changes are specific to neuropathic pain or whether they may be common to other chronic pain.